McQuay RCS 025D Installation Manual

Installation and Maintenance Manual IM 893-1

RoofPak™ Singlezone Roof Mounted
Heating and Cooling Units

RPS/RDT/RFS/RCS 015D – 140D
R-410A Refrigerant and MicroTech® III Unit Controller

Group: Applied Systems

Part Number: IM 893

Date: November 2009

Contents

Introduction .............................................................. 3

Unit Nameplate ................................................... 3

Compressor Nameplate...................................... 3

Gas Burner Nameplate ....................................... 3

Hazard Identification Information ........................ 3

Unit Description .................................................. 4

Refrigeration Piping ............................................ 6

Control Locations................................................ 7

Control Panel ...................................................... 9

Controls, Settings, and Functions..................... 16

Condenser Fan Arrangement ........................... 19

Mechanical Installation .......................................... 20

Unit Clearances ................................................ 20

Ventilation Clearance........................................ 21

Overhead Clearance......................................... 21

Roof Curb Assembly and Installation................ 22

Post and Rail Mounting..................................... 25

Rigging and Handling ....................................... 25

Reassembly of Split Units................................. 27

Unit Piping ........................................................ 35

Steam Coil Piping ............................................ 36

Damper Assemblies.......................................... 38

Cabinet Weather Protection.............................. 40

Installing Ductwork............................................ 40

Installing Duct Static Pressure Sensor Taps .... 41

Installing Building Static Pressure Sensor Taps 42

Electrical Installation ............................................. 43

Field Power Wiring............................................ 43

Field Control Wiring .......................................... 46

Preparing Unit for Operation ................................. 47

Spring Isolated Fans......................................... 47

Adjusting Spring Mounts................................... 47

Relief Damper Tie-Down .................................. 48

Adjustment of Seismic Restraints ..................... 48

Adjusting Scroll Dampers ................................. 48

Adjusting Supply Fan Thrust Restraints ........... 49

Sequences of Operation ........................................ 50

Power-up .......................................................... 50

Fan Operation................................................... 50

Economizer Operation ...................................... 51

Mechanical Cooling Operation.......................... 51

Heating ............................................................. 52

MicroTech III Controller Operation ....................... 53

Using the Keypad/Display................................. 53

Passwords ........................................................ 53

Navigation Mode............................................... 54

Edit Mode ......................................................... 54

Wiring Diagrams ..................................................... 55

Unit Options ............................................................ 73

Control Actuators .............................................. 73

Enthalpy Control ............................................... 73

Modulating Hot Gas Reheat ............................. 75

Hot-Gas Bypass (HGBP) .................................. 77

External Time Clock.......................................... 77

Smoke and Fire Protection ............................... 77

Smoke Detectors .............................................. 78

Emergency Shutdown ...................................... 78

Freeze Protection............................................. 78

Field Output Signals......................................... 79

Entering Fan Temperature Sensor................... 80

Duct High Pressure Limit ................................. 80

Variable Frequency Drive Operation ................ 80

Convenience Receptacle/Section Lights.......... 80

Optional Low Ambient Compressor

Operation ......................................................... 81

Variable Frequency Drive Operation ................ 82

Convenience Receptacle/Section Lights.......... 82

DesignFlow™ Outdoor Air Damper Option ...... 82

Propeller Exhaust Fan Option .......................... 85

Exhaust Fan On/Off Control............................. 88

Ultraviolet Lights Option ................................... 88

Check, Test, and Start Procedures ...................... 92

Servicing Control Panel Components .............. 92

Before Start-up................................................. 92

Power Up ......................................................... 92

Fan Start-up ..................................................... 93

Economizer Start-up ........................................ 93

Compressor Startup ......................................... 93

Scroll Compressor Rotational Direction ........... 94

Heating System Startup ................................... 95

Air Balancing .................................................... 96

Sheave Alignment ............................................ 96

Drive Belt Adjustment....................................... 96

Mounting and Adjusting Motor Sheaves .......... 97

Final Control Settings.......................................... 100

Maintenance ......................................................... 104

Servicing Control Panel Components ............ 104

Planned Maintenance .................................... 104

Unit Storage ................................................... 104

Gas Furnace .................................................. 105

Bearing Lubrication ........................................ 105

Propeller Exhaust Fan.................................... 107

Setscrews....................................................... 107

Supply Fan Wheel-to-Funnel Alignment ........ 108

Scroll Compressor Piping............................... 110

All-Aluminum Condenser Coils ...................... 111

Refrigerant Charge......................................... 112

Servicing Refrigerant Sensors or Switches.... 112

Winterizing Water Coils.................................. 112

Control Panel Components ............................ 113

Replacement Parts List ....................................... 117

Service and Warranty Procedure ....................... 118

Replacement Parts......................................... 118

Scroll Compressor.......................................... 118

Replacing a Portion of a Tandem or Trio ....... 118

In-Warranty Return Material Procedure ......... 119

Limited Product Warranty (North America)....... 120

Exceptions...................................................... 120

Assistance...................................................... 120

Sole Remedy.................................................. 120

Rooftop Equipment Warranty Regist. Form ...... 121

Quality Assurance Survey Report...................... 124

Introduction

R P S – 080 D S E

RoofPak

Unit configuration
P = Heating, mechanical cooling
F = Heating, future mechanical cooling
C = Condensing section only
D = Draw through cooling

Blow through cooling = S
Draw through cooling = T

Heat medium
A = Natural gas
E = Electric
S = Steam
W = Hot water
Y = None (cooling only)

Design vintage

Nominal capacity (tons)
RPS, RFS, RCS, RDT: 015, 020, 025, 030, 035, 040, 042, 045, 050,
060, 062, 068, 070, 075, 080, 085, 090, 100, 105, 110, 120, 125, 130,
140

Cooling coil size
S=Standard (low airflow)
L =Large (high airflow)

This manual provides general information about the “D”
vintage McQuay RoofPak applied rooftop unit, models RPS,
RDT, RFS and RCS. In addition to an overall description of
the unit, it includes mechanical and electrical installation
procedures, commissioning procedures, sequence of operation
information, and maintenance instructions. For further
information on the optional forced draft gas-fired furnace,
refer to IM 684 or IM 685.

The MicroTech III applied rooftop unit controller is available
on “D” vintage applied rooftop units. For a detailed
description of the MicroTech III components, input/output
configurations, field wiring and information on using and
programming the MicroTech III unit controller, refer to OM

920.

For a description of operation and information on using the
keypad to view data and set parameters, refer to the

appropriate program-specific operation manual (see Figure 1).

Table 1: Program Specific Rooftop Unit Literature

Operation manual

number

VFDs

Rooftop unit control configuration

McQuay 208 - 460 V OM 844

McQuay 575 V OM 895

Non-McQuay See vendor manuals

Unit Nameplate

The unit nameplate is located on the outside lower right corner
on the main control box door. It includes the unit model
number, serial number, unit part number, electrical
characteristics, and refrigerant charge.

Introduction

Compressor Nameplate

On units that utilize the tandem compressor design, each
compressor includes an individual nameplate along with a
nameplate identifying the tandem compressors.

On units that utilize the trio compressor design, each
compressor includes an individual nameplate. There is no
nameplate identifying the trio compressors.

Gas Burner Nameplate

On units that include gas heat, the nameplate is located on the
lower right corner on the main control box door. It includes the
burner model number, minimum/maximum input, maximum
temperature rise, and minimum CFM.

Hazard Identification Information

DANGER

Dangers indicate a hazardous situation which will result in
death or serious injury if not avoided.

WARNING

Warnings indicate potentially hazardous situations, which can
result in property damage, severe personal injury, or death if
not avoided.

CAUTION

Cautions indicate potentially hazardous situations, which can
result in personal injury or equipment damage if not avoided.

Figure 1: Nomenclature

McQuay IM 893-1 3

Introduction

RPS/RDT

Unit Description

Figure 2: RPS/RDT/RFS/RCS Unit

Typical Component Locations

Figure 2 shows an RPS/RDT/RFS/RCS unit. Figure 3 shows a
typical RPS unit with the locations of the major components.
Figure 4 on page 5 shows a typical RDT unit with the locations
of the major components. These figures are for general
information only. See the project’s certified submittals for
actual specific dimensions and locations.

Figure 3: Typical Component Locations—RPS Units

1.5" NPT Drain

Condenser
control panel
(RCS only)

4 McQuay IM 893-1

Figure 4: Component Locations—RDT Units

1.5 NPT drain

Introduction

McQuay IM 893-1 5

Introduction

O

A Compressor (1, 2, or 3 per circuit) †
B Discharge line †
C Condenser coil †
D Evaporator coil *
E Manual shutoff valve †
F Filter-drier †
H Sightglass †

I Liquid line *†
J Suction line *†
K Thermal expansion valve *
L Distributor *
M Drop solenoid valve *
N Hot gas bypass valves (optional) *
O Hot Gas bypass piping (optional) *†

*Supplied on RFS units
†Supplied on RCS units

Refrigeration Piping

This section presents the unit refrigeration piping diagrams for
the various available configurations.

Figure 5: Circuit Schematic

Figure 6: Condenser Piping, Scroll Compressors, 2 to 3 Compressors per Circuit are Provided (6 Compressors Shown)

6 McQuay IM 893-1

Control Locations

R eturn air

economizer

Filter

se ction

Supply

fan

Heat

DX

se ction

Discharge

plenum
se ction

Condensor

se ction

RAT

LT11

(optio na l)

S11,
REC11

OAE

ACT 3

PC5

S10, R EC10

LT10

HL22

EFT

SD1

VM1

DAT

ACT5 (optional)

HT R 1-2, HTR3-4 (optional)

(optional)

(optional)

(optional)

(optional)

(optional)

se ction

se ction

FS1

(optional)

C19

OAT

AC T6 (optional)

RAE (optional)

SD2

(optional)

PC7

C11, 12
(optional)

SC11, 12
(optional)

Introduction

Figure 7 (RPS Units) and Figure 8 on page 8 (RDT Units)
show the locations of the various control components mounted
throughout the units. See “Control Panel” on page 9 for the
locations of control components mounted in control panels.

Figure 7: Control Locations—RPS units

Additional information is included in Table 2 on page 16 and
the wiring diagram legend, which is included in “Wiring
Diagrams” on page 55.

McQuay IM 893-1 7

Introduction

Economizer

Filter

DX

Heat

section

Supply fan

discharge

plenum

section

Condenser

C19, 20

RAT

LT11 (optional)

S11, REC11

SD2

RAE

ACT3

PC5

OAE

VM1

LT10 (optional)

DAT

OAT

SC11, 21
(optional)

C11, 21
(optional)

(optional)

HTR3-4 (optional)

section

section

section

return air

(optional)

(optional)

(optional)

(optional)

C9

FS1

(optional)

HTR1-2, U1/U2

S10, REC10 (optional)

SD1 (optional)

ACT6

Figure 8: Control Locations—RDT Units

8 McQuay IM 893-1

Control Panel

Prop exhaust/ return fan

Introduction

The unit control panels and their locations are shown in the
following figures. These figures show a typical unit
configuration. Specific unit configurations may differ slightly

Figure 9: Control Panel Locations

from these figures depending on the particular unit options.
See “Wiring Diagrams” on page 55 for the legend and
component description.

McQuay IM 893-1 9

Introduction

Figure 10: Typical Main Control Panel, 045D to 075D, 460 Volt

10 McQuay IM 893-1

Figure 11: Typical Main Control Panel, 080D to 140D, 460 Volt

Introduction

McQuay IM 893-1 11

Introduction

S3

FSG

FSG Time

LS1

LS2

AS

IT

TD10

R22

R20

R23 R21

TB11

AFD20 GND

M51 M52 M53

Figure 12: Typical Gas Heat Panel, 1000 MBh (High TD) Figure 13: Typical Prop Exhaust Panel, 3 Fans, 460 Volt

Figure 14: VFD Bypass Panel, 40 HP, 460 Volt

12 McQuay IM 893-1

Figure 15: RCS Control Panel with MicroTech III, RPS 045D to 075D

Figure 16: RCS Control Panel with MicroTech III, RPS 080D to 140D

Introduction

McQuay IM 893-1 13

Introduction

GLG3

DS3

M41M43

FB41FB42FB43

H53

TB11

M31M32M33

FB31FB32FB33

M42

GLG3

DS3

M41M42M43

FB41FB42FB43

H53

TB11

M34M44

M31M32M33

FB31FB32FB33

FB34FB44

Figure 17: Electric Heat Panel, Sizes 045D to 75D Figure 18: Electric Heat Panel, Sizes 080D to 140D

14 McQuay IM 893-1

Figure 19: Harness Plug Connector Detail

LT OP1 LT OP2

LT11LT1 0

COMP6COMP5

COMP3 COMP4

COMP1 COMP2

DFRH DFLH OPEN4

SD1 SD2

GSHT1 GSHT2

HL22 OPEN3

OAE PC7PC5

ACT3 OPEN2

SV12 SV56

AFD10 AFD20

FP1 OPEN1EPTS

RATS OATSDATS

Introduction

McQuay IM 893-1 15

Introduction

Controls, Settings, and Functions

Table 2 below lists all of the unit control devices. Included in
the table are the device symbol, a description of the device, its
function, and any reset information, its location, any device
setting, any setting ranges, differentials, and the device part
number.

Table 2: Controls, Settings, and Functions

Symbol Description Function Reset Location Setting Range Differential Part no.

CS1 & 2 Switch (toggle),

refrigerant circuit

DAT Discharge air

temperature
sensor

DHL Duct high limit

switch

EFT Entering fan air

temperature
sensor

FP1, 2 Frost protection Senses DX coil temperature

FS1 Freezestat Shuts off fans, opens heating

HP1, 2 High pressure

control

LP1, 2 Low pressure

control

MCB Main control board Processes input information N/A Main control

MP1–6 Compressor

motor protector

OAE Enthalpy control

(electro­mechanical)

Enthalpy control
(electronic)

OAT Outside air

temperature
sensor

PC5 Dirty filter switch Senses filter pressure drop Auto First filter

PC6 Dirty filter switch Senses filter pressure drop Auto Final filter

PC7 Airflow proving

switch

RAE Return air

enthalpy sensor

RAT Return air

temperature
sensor

Shuts off compressor control
circuits manually

Senses discharge air
temperature

Prevents excessive VAV duct
pressures; shuts off fan

Senses entering fan air
temperature

for frost protection

valve, and closes outdoor
damper if low air temperature
at coil is detected

Stops compressor when
refrigerant discharge pressure
is too high

Stops compressor when
suction pressure is too low

Senses motor winding
temperature, shuts off
compressor on high
temperature.

Returns outside air dampers to
minimum position when
enthalpy is too high

Returns outside air dampers to
minimum position when
outside air enthalpy is higher
than return air empalthy
(use RAE)

Senses outside air
temperature

Senses supply fan pressure to
prove airflow

Used to compare return air
enthalpy to outside air
enthalpy (used with OAE)

Senses return air temperature N/A Return air

N/A Main control

N/A Discharge air

Auto Main control

N/A Inlet of supply

Auto DX coil 30° +/- 6° open

Auto Heating

Manual

(relay

latched)

Auto Compressor See page 112. N/A 45 psi with low

Auto at

3400
ohms

Auto Economizer

Auto Economizer

N/A N/A N/A 060004705

Auto Supply fan

N/A Economizer

panel

section

panel

fan

section

Compressor See page 112. N/A 150 psi 403585001

box

Compressor
junction box

section

section

section

section

section

section

section

N/A N/A N/A 01355000

N/A N/A 060004705

3.5" w.c

(871.8 Pa)

N/A N/A 060004705

45° +/- 6° close

38°F (3°C)

or as required

N/A N/A N/A 060006101

9 K–18 K ohms 700 ohms cold N/A 044691509

“B” or as required A–D Temperature:

Fully CW past “D”

(when used

with RAE)

As required .05-5" w.c.

As required .05-5" w.c.

.10" w.c. (25 Pa) .05-5" w.c.

N/A N/A N/A 049262202

N/A N/A 060004705

0.05–5.0" w.c.

(12.5–1245.4 Pa)

N/A 15° 113073401

35°F–45°F

(2°C–7°C)

A–D N/A 049262201

(12.5–1245.4 Pa)

(12.5–1245.4 Pa)

(12.5–1245.4 Pa)

.05" w.c.

(12.5 Pa), fixed

12°F (7°C),

fixed

amb. option

/50 psi

3.5°F (2°C)
Humidity:

5% fixed

.05" w.c.

(12.5 Pa)

.05" w.c.

(12.5 Pa)

.05" w.c.

(12.5 Pa), fixed

065493801

065830001

403585501/

403585101

030706702

065493801

065493801

060015801

16 McQuay IM 893-1

Introduction

Table 2: Controls, Settings, and Functions (continued)

Symbol Description Function Reset Location Setting Range Differential Part no.

SD1 Smoke detector,

supply air

SD2 Smoke detector,

return air

SPS1 Static pressure

sensor duct #1

SPS2 Static pressure

sensor duct #2

Static pressure
sensor: building
(space) pressure

S1

System switch

S7 ON-OFF-AUTO

switch

SV1-2 Drop solenoid Shuts liquid line when

FanTrol

The FanTrol, provided on all units, is a method of head
pressure control that automatically cycles the condenser fans
in response to ambient air temperature. This feature maintains
head pressure and allows the unit to run at low ambient air
temperatures.

Initiates unit shutdown if
smoke is detected

Initiates unit shutdown if
smoke is detected

Converts static pressure
signals to voltage signals

Converts static pressure
signals to voltage signals

Converts static pressure
signals to voltage signals.

Shuts off entire control circuit
(except crankcase heaters)

Used to manually switch unit N/A Main control

compressor is off

Manual Discharge air

section

Manual Return air

section

N/A Main control

box

N/A Main control

box

N/A Main control

box

N/A Main control

box

box

N/A Discharge air

section

RPS/RDT and RCS units have two independent refrigerant
circuits with one to four condenser fans being controlled
independently by the ambient air temperature of each circuit.
See the following sections for sequence of operation for

condenser fans with FanTrol.

N/A N/A N/A 04925001

N/A N/A N/A 04925001

N/A 0–5" w.c.

(0–1245.4 Pa)
1–6 V (dc) out

N/A 0–5" w.c.

(0–1245.4 Pa)
1–6 V (dc) out

N/A -025–0.25" w.c.

(-62.3–62.3 Pa)

1–5 V (dc) out

N/A N/A N/A 001355000

N/A N/A N/A

N/A N/A N/A 049266502

N/A 049545007

N/A 049545007

N/A 049545006

Table 3: R-410A FanTrol Setpoints in °F with MicroTech III Controls

Degrees Farenheit

Unit Size

Setpoint Differential Setpoint Differential Setpoint Differential

015D 70 5

020D 70 5

025D 60 5

030D 75 5

035D 70 5

040D 65 5

042D 65 5

045D 65 5

050D 65 5

060D 60 5

062D 70 5

068D 70 5

070D 75 5 90 35

075D6558559035

080D 75 5 90 35

085D 70 5 90 35

090D6058559035

100D6058559035

105D5058059035

110D6559059035

120D6558559035

125D6558559035

130D6058559035

140D5558059035

* PC13/23 Cut in = 450 psig (125 degree sat.)

Cut out = 275 psig (90 degree sat.)

D07 D08 PC13/PC23

1

McQuay IM 893-1 17

Introduction

Table 4: R-410A Fan Cycling Setpoints in °F with No Controls

RPS RCS
RDT RPR

015D TC12 65 70 5 TC12 Controls 1 Fan
020D TC12 65 70 5 TC12 Controls 1 Fan
025D TC12 55 60 5 TC12 Controls 1 Fan
030D TC12 70 75 5 TC12 Controls 1 Fan
035D TC12 65 70 5 TC12 Controls 1 Fan
040D TC12 60 65 5 TC12 Controls 1 Fan
042D TC12 60 65 5 TC12 Controls 1 Fan
045D TC12 60 65 5 TC12 Controls 1 Fan
050D TC12 60 65 5 TC12 Controls 1 Fan
060D TC12 55 60 5 TC12 Controls 1 Fan
062D TC12 65 70 5 TC12 Controls 1 Fan
070D TC12 65 70 5 TC12 Controls 1 Fan

075D TC12 60 65 5 TC12 Controls 1 Fan

080D TC12 70 75 5 TC12 Controls 1 Fan

090D TC12 55 60 5 TC12 Controls 1 Fan

100D TC12 55 60 5 TC12 Controls 1 Fan

110D TC12 60 65 5 TC12 Controls 1 Fan

120D TC12 60 65 5 TC12 Controls 1 Fan

125D TC12 60 65 5 TC12 Controls 1 Fan

140D TC12 50 55 5 TC12 Controls 1 Fan

* PC13/23 Cut in = 450 psig (125 degree sat.), cut out = 275 psig (90 degree sat.). PC13/23 setpoints are fixed.

Control ID

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 80 85 5 TC14 Controls 1 Fan

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 80 85 5 TC14 Controls 1 Fan

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 80 85 5 TC14 Controls 1 Fan

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 85 90 5 TC14 Controls 1 Fan

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 80 85 5 TC14 Controls 1 Fans

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 80 85 5 TC14 Controls 1 Fan

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

TC14 75 80 5 TC14 Controls 2 Fans

PC13/PC23 90 125 35 PC13/PC23 Controls 1 Fan*

Cut Out Cut In Differential

Degrees °F

Notes

18 McQuay IM 893-1

Condenser Fan Arrangement

11

12

11

13

23

12

22

21

24

14

11

12

21

22

11

12

21

22

11

12

21

22

11

12

21

22

23

13

11

13

23

12

22

21

Introduction

Table 5 below shows the condenser fan numbering
conventions and locations for each unit size.

Table 5: Condenser Fan Arrangement

Unit size Refrigerant circuit Arrangement Unit size Refrigerant circuit Arrangement

1

015D -

025D

2

1

020D -

042D

2

1

045D

2

1

075D -

090D

2

1

100D

2

1

110 D

2

050D -

060D

062D

070D -

080D

1

120D

2

1

125D

2

1

140D

2

1

2

1

2

1

2

McQuay IM 893-1 19

Mechanical Installation

*Condenser coil replacement is simplified

if the following temporary access clearance
can be arranged:

015D - 025D 61"
030D - 062D 83"
070D - 100D 106"
110D - 140D 38"

*

Mechanical Installation

The installation of this equipment shall be in accordance with
the regulations of authorities having jurisdiction and all
applicable codes. It is the responsibility of the installer to
determine and follow the applicable codes.

Note: Low head pressure may lead to poor, erratic refrigerant

feed control at the thermostatic expansion valve. The
units have automatic control of the condenser fans
which should provide adequate head pressure control
down to 50°F (10°C) provided the unit is not exposed to
windy conditions. The system designer is responsible
for assuring the condensing section is not exposed to
excessive wind or air recirculation.

CAUTION

Sharp edges on sheet metal and fasteners can cause
personal injury.

This equipment must be installed, operated, and serviced
only by an experienced installation company and fully
trained personnel.

Figure 20: Service Clearances

Receiving Inspection

When the equipment is received, all items should be carefully
checked against the bill of lading to be sure all crates and
cartons have been received. If the unit has become dirty

during shipment (winter road chemicals are of particular
concern), clean it when received.

All units should be carefully inspected for damage when
received. Report all shipping damage to the carrier and file a
claim. In most cases, equipment is shipped F.O.B. factory and
claims for freight damage should be filed by the consignee.

Before unloading the unit, check the unit nameplate to make
sure the voltage complies with the power supply available.

Unit Clearances

Service Clearance

Allow service clearance approximately as indicated in
Figure 20. Also, McQuay recommends providing a roof
walkway to the rooftop unit as well as along at least the two
sides of the unit that provide access to most controls and
serviceable components.

20 McQuay IM 893-1

Ventilation Clearance

24" (610 mm)
maximum

96" (2438 mm)

minimum,

top of unit to

permanent

overhead

obstruction

24" (610 mm)
maximum

Overhead
canopy

9" (229 mm)
minimum to flue box,
typical all sides

Flue box

Mechanical Installation

Below are minimum ventilation clearance recommendations.
The system designer must consider each application and
provide adequate ventilation. If this is not done, the unit will
not perform properly.

Unit(s) surrounded by a screen or a fence:

The bottom of the screen or fence should be at least 1 ft.

1

(305 mm) above the roof surface.

2 The distance between the unit and a screen or fence should

be as described in “Service Clearance” on page 20. See also
Figure 20 on page 20.

3 The distance between any two units within a screen or

fence should be at least 120" (3048 mm).

Unit(s) surrounded by solid walls:

1 If there are walls on one or two adjacent sides of the unit,

the walls may be any height. If there are walls on more than
two adjacent sides of the unit, the walls should not be
higher than the unit.

2 The distance between the unit and the wall should be at

least 96" (2438 mm) on all sides of the unit.

3 The distance between any two units within the walls should

be at least 120" (3048 mm).

Do not locate outside air intakes near exhaust vents or other
sources of contaminated air.

If the unit is installed where windy conditions are common,
install wind screens around the unit, maintaining the
clearances specified (see Figure 21). This is particularly
important to prevent blowing snow from entering outside air
intake and to maintain adequate head pressure control when
mechanical cooling is required at low outdoor air
temperatures.

Overhead Clearance

1 Unit(s) surrounded by screens or solid walls must have no

overhead obstructions over any part of the unit.

2 The area above the condenser must be unobstructed in all

installations to allow vertical air discharge.

3 The following restrictions must be observed for overhead

obstructions above the air handler section (see Figure 21):

a There must be no overhead obstructions above the

furnace flue, or within 9" (229 mm) of the flue box.

b Overhead obstructions must be no less than 96"

(2438 mm) above the top of the unit.

c There must be no overhead obstructions in the areas

above the outside air and exhaust dampers that are
farther than 24" (610 mm) from the side of the unit.

Figure 21: Overhead Clearance

McQuay IM 893-1 21

Mechanical Installation

See DETAIL A

(INSIDE)
015D - 025D = 52.00
030D - 068D = 64.00
070D - 105D = 83.00

110D - 140D = 120.00

(INSIDE)

Roof Curb Assembly and Installation

Locate the roof curb and unit on a portion of the roof that can
support the weight of the unit. The unit must be supported to
prevent bending or twisting of the machine.

If building construction allows sound and vibration into the
occupied space, locate the unit over a non-critical area. It is

the responsibility of the system designer to make adequate
provisions for noise and vibration in the occupied space.

WARNING

Mold can cause personal injury. Some materials such as
gypsum wall board can promote mold growth when damp.
Such materials must be protected from moisture that can enter
units during maintenance or normal operation.

Install the curb and unit level to allow the condensate drain to
flow properly and allow service access doors to open and close
without binding.

Integral supply and return air duct flanges are provided with
the RPS/RFS roof curb, allowing connection of duct work to
the curb before the unit is set. The gasketed top surface of the
duct flanges seals against the unit when it is set on the curb.

Figure 22: RCS Roof Curb Assembly

These flanges must not support the total weight of the duct
work. See “Installing Ductwork” on page 40 for details on duct
connections. It is critical that the condensate drain side of the
unit be no higher than the opposite side.

Assembly of a typical RPS/RDT roof curb is shown in
Figure 23 on page 23. Parts A through K are common to all
units having bottom supply and return openings. Depending on
the unit length, Parts L and M may be included with the roof
curb kit to create the correct overall curb length. Figure 22
shows the assembly of the RCS roof curb.

RCS Assembly instructions (Figure 22)

1 Set curbing parts (A) in place making sure that the

orientation complies with the assembly instructions. Check
alignment of all mating bolt holes.

2 Bolt curbing parts together using fasteners provided.

3 Curb must be level from side to side and over its length.

4 Weld curbing in place. Caulk all seams watertight and

insulate between channels.

5 Flash curbing into roof as shown in Detail C.

RPS/RDT Assembly instructions (Figure 23 on
page 23)

1 Set curbing parts A through K per dimensions shown over

2 If applicable, set other curbing parts (D, L, M, etc.) in place

3 Bolt curbing parts together using fasteners provided.

4 Square entire curbing assembly and securely tighten all

22 McQuay IM 893-1

roof opening or on a level surface. Note location of return
and supply air openings.

making sure that the orientation complies with the
assembly instructions. Check alignment of all mating bolt
holes. See Detail A.

Tighten all bolts finger tight.

bolts.

5 Position curb assembly over roof openings. Curb must be

level from side to side and over its length. Check that top
surface of the curb is flat with no bowing or sagging.

6 Weld curbing in place. Caulk all seams watertight. Remove

backing from 0.25" (6 mm) thick × 1.50" (38 mm) wide
gasketing and apply to surfaces shown by cross-hatching.

7 Flash curbing into roof as shown in Detail B.

8 Parts E and F are not required on units with no return shaft

within the curb perimeter.

9 Parts G and H are not required on units with no supply shaft

within the curb perimeter.

10 Be sure that electrical connections are coordinated (see

Figure 24).

Figure 23: RPS/RFS Roof Curb Assembly

Mechanical Installation

Table 6: RPS/RFS Roof Curb Assembly Dimensions

Unit size Return Fan

015D – 042D 2 x 15" FC

30" AF
40" AF

None
045D – 075D All units 38.0 965 87.0 2210 030D 56.2 1427 030D 20 508
080D – 140D All units 62.0 1575 87.0 2210 035D – 040D 57.3 1455 035D – 040D 20 508

Note: These dimensions do not apply to units with energy recovery wheels.

X Y

in mm in mm in mm in mm

2083

82

610

24

1930

76

762

30

36|

24

914
610

78
82

1981
2083

Unit size

015D – 025D 53.6 1361 015D – 025D 20 508

045D – 068D 61.0 1594 045D – 075D 28.0 711
070D – 105D 74.0 1880 080D – 090D 38.0 965
110D – 140D 99.0 2514 100D – 140D 46.0 1168

Z

Unit size

W

McQuay IM 893-1 23

Mechanical Installation

Unit length minus 6.4

12.1

See Detail A

Detail A

3.4

5.1

0.9 Dia.
K.O.

3.0 Dia.
K.O.

4.6

4.8

2.0

2.1

4.3

3.1

9.7

76.0

7.5

20.0

1.5

6.8

OPNG

B

2Typ

A

A

D

C

D

4Typ

A

SA

OPNG

RPS only

RA

Figure 24: Typical Power Wire Entrance, Curb View (RPS/RFS 045D to 140D shown, See Project Certified Drawings)

24 McQuay IM 893-1

Post and Rail Mounting

* Beam can extend beneath unit no more than 5” to allow adequate space
for duct connections and electrical entry.

Unit has either four or six lifting points (four-point shown below).

Rigging cables must be at least as long as distance “A”

Spreader bars
required

Lift only as indicated

Caution: Lifting points may not

be symmetrical to center of
gravity of unit. Balast or unequal
cable lengths may be required.

A

Mechanical Installation

When mounting by post and rail, run the structural support the
full length of the unit. Locate the structural member at the base
of the unit as shown in Figure 25, assuring the I-beam is well

supported by the structural member.

CAUTION

The unit must be level side to side

and over the entire length.

Equipment damage can result if the unit is not level.

If resilient material is placed between the unit and the rail,
insert a heavy steel plate between the unit and the resilient
material to distribute the load. Seal cabinet penetrations
(electrical, piping, etc.) properly to protect against moisture
and weather.

Figure 25: Post and Rail Mounting

99"

MAX.

1 Support the unit well along the length of the base rail.

2 Level the unit (no twists or uneven ground surface).

3 Provide proper drainage around the unit to prevent flooding

of the equipment.

4 Provide adequate protection from vandalism, mechanical

contact, etc.

5 Securely close the doors.

6 If there are isolation dampers, make sure they are properly

installed and fully closed to prevent the entry of animals
and debris through the supply and return air openings.

7 Cover the supply and return air openings on units without

isolation dampers.

Figure 26 shows an example of the rigging instruction label
shipped with each unit.

WARNING

Use all lifting points. Improper lifting can cause severe personal
injury and property damage.

Figure 26: Rigging and Handling Instruction Label

Rigging and Handling

Lifting brackets with 2" (51 mm) diameter holes are provided
on the sides of the unit.

Use spreader bars, 96" to 100" (2438 to 2540 mm) wide to
prevent damage to the unit cabinet. Avoid twisting or uneven
lifting of the unit. The cable length from the bracket to the
hook should always be longer than the distance between the
outer lifting points.

If the unit is stored at the construction site for an intermediate
period, take these additional precautions:

McQuay IM 893-1 25

CAUTION

Lifting points may not be symmetrical to the center of gravity of
the unit. Ballast or unequal cable lengths may be required.

Mechanical Installation

4 Lifting Points

A

Lifting Points

Refer to Figure Note: and Figure 28 and the following
calculations to determine whether a four or six point lift is
required.

X = distance from the entering air end of the unit (or shipping
section) to the first lifting lug in the direction of air flow.

For all unit or shipping sections with outdoor air/return air
options, X = 48"

For shippings sections without outdoor air/return air
options, X= 0

Y = distance from condenser or leaving air end of unit to the
last lifting lug.

For all units or shipping sections with condensers, Y = 25.6
(sizes 30-40), Y = 13.9 (sizes 15-25), Y = 36.5 (sizes 50-68),
Y = 30.0 (sizes 70-105), or Y = 38.0 (sizes 110-140).

For all units or shipping sections without condensers, Y = 0.

Installation

Z = total base rail length of the units.

Note: Z excludes hoods and overhung parts extending past

base rails of the unit.

Figure 27: RPS/RDT Lifting Points

A = Z - X - Y

If A < 288", 4-point lift is sufficient

If A > 288", 6-point lift is required

B = distance from first lifting lug to middle lifting lug on units
with 6-point lift.

B = A / 2 +/- 48"

Note: Middle lifting lug may be installed on either side of the

midpoint to avoid interference with condensate drains.

RDT 050D–140D: B Min. = 72” (1829 mm)
RPS 080D–105D: B Min: = 96” (2348 mm)
RPS 110D–140D: B Min: = 120” (3048 mm)

Figure 28: RCS or Condenser Factory Split at Condenser

B

015D – 042D: B (min.) = 82" (2362 mm)
045D – 068D: B (min.) = 59" (1448 mm)
070 B (min.) = 82" (2362 mm)

D – 105D:

110D – 140D: B (min.) = 115" (2870 cm)

26 McQuay IM 893-1

Mechanical Installation

Z

4 Lifting Points

Z

B

045D–068D: B Min. = 72 (1829 mm)
070D–105D: B Min. = 96 (2438 mm)
110D–140D: B Min. = 120 (3048 mm)

Figure 29: RPS Factory Split at Supply Fan Section

refrigerant piping intact so field evacuation and charging is not
required. Detailed instructions are on pages 27 to 29.

A single nameplate is attached to the air handler section and
power is fed to both sections through the main control box, as
in a non-split RPS/RDT unit.

Field reassembly of an RPS/RDT unit that has shipped split at
the fan takes place in three phases: (1) setting the sections
(2) mechanically recoupling the cabinet, and (3) reconnecting
power and control wiring.

Phase I. Set sections (Figure 30)

1 Remove top cap and save for Step 3.

2 Remove screws on fan panel, leaving retainer clips in place

to secure bulkhead. Save screws for Phase II, Step5.

3 Remove plywood and retaining angles from unit and

discard.

4 Carefully lower both sections of unit (fan end and

discharge end) into place, making sure the roof curb
engages the recesses in the unit base.

Reassembly of Split Units

Although RoofPak units typically ship from the factory as
complete units, they may be split at the factory in one of two
possible configurations; see (1) “RPS Factory Split at Fan”
below and (2) “RFS/RCS Permanent Split Systems” on page

30.

RPS Factory Split at Fan

The RPS unit is factory split at the fan section and ships as two
pieces, split at the supply fan bulkhead, to recouple together on
the roof. Like the RPS/RDT unit factory split at the condenser,
this configuration is ordered if shipping length or weight
limitation prevents a packaged RPS/RDT from being ordered.
Splitting at the fan has the advantage of leaving all factory

McQuay IM 893-1 27

Mechanical Installation

Remove top cap and
save for reassembly.

Remove plywood and retaining
angles from unit and discard.

Discharge end of unit

Fan end of unit

Remove screws on fan panel,
leaving retainer clips in place.
Save screws for reassembly.

Reinstall top cap
saved in step 1

Caulk ends
of splice cap

See detail

Splice cover,

provided

#10 screws,

provided

Nut clip-on,
provided

Caulk
vertical
seam

Install screws
(.25 to 20 × .75)
saved from step 1

Figure 30: Set Sections - Steps 1-4, RPS Factory Split at Supply Fan

Phase II. Reassemble cabinet (Figure 31)

1

Reinstall top cap removed in Phase I, Step 1.

2 Caulk (watertight) ends of splice cap.

3 Caulk (watertight) vertical seam.

Figure 31: Reassemble Cabinet

4 Install #10 screws (provided).

5 Install screws (.25–20 × .75) removed in Phase I, Step 2

6 Install splice cover (provided).

28 McQuay IM 893-1

Phase III. Reconnect Power and Control Wiring

If applicable, install as shown
with provided fasteners.

After routing wires,
install inner raceway
cover (see step 6).

3.72 ref.
(94 mm)

Capped

refrigerant

lines

Mechanical Installation

The DX coil/condenser section contains power and control
harnesses that have their excess length in the blank or heat
section, which normally is immediately downstream of the fan.
Once the sections are physically reconnected, the ends of the
power harness are fed back through the unit base into the
junction box, per the unit’s electrical schematics.

CAUTION

Connect the power block correctly and maintain proper
phasing. Improper installation can cause severe equipment
damage.

1 Make electrical connections and reinstall inner raceway

cover as shown in Figure 32.

Figure 32: Electrical Connections/Cover Installation

When power wire reconnection is complete, reinstall the

2

inner raceway cover in the blank or heat section. Figure 32
shows a typical installation of the raceway cover.

3 Run the control harnesses by removing the external

raceway covers on either side of the unit split.

4 Remove the excess harness length from the external

raceway on the DX side of the split; then route along the
raceway through the bushed hole in the fan section and into
the junction box where control wiring terminal blocks are
provided for reconnection.

5 Make all electrical connections per the unit’s electrical

schematics.

6 Reinstall the external raceway covers after routing of the

control wires is complete.

7 Draw through cooling coils only. Reconnect refrigerant

piping. These refrigerant circuits for these units are shipped
with a holding charge only. Figure 33 illustrates what the
installer sees at the shipping split

a To bridge the gap and connect the piping, remove the

refrigerant piping caps and add fittings and copper
tubing, as required.

b Evacuate and charge the unit. See page 32 for further

details.

Figure 33: Refrigerant Lines

McQuay IM 893-1 29

Mechanical Installation

RFS/RCS Permanent Split Systems

The RFS air handler section and RCS condenser section ship
as two separate units. This configuration is ordered when the
condenser is intended to remain separated by a short distance
from the air handler because of space or structural constraints.

Small traps should be provided at the base of each major
vertical gas riser to assist in the collection of oil. If vertical
risers exceed more than 25 feet, install a small trap at the
midpoint and at a maximum of 20 foot intervals.

On all units, refrigerant piping is terminated near the exterior
of the cabinet for convenient field piping between the RCS and
RFS units, and all necessary refrigeration components are
provided (except the field-installed hot gas bypass valve).
Detailed instructions are on pages 32 to 35.

The hot gas bypass valve should be located at the high point of
the piping, so that refrigerant does not accumulate at the valve
when it is shut, and also should be located as close to the RCS
as possible. Minimize pipe bends (especially those that
accumulate refrigerant) as much as possible. Connect the
pressure sensing tap to the suction line.

Piping Recommendations

All field piping, wiring, and procedures must be performed in
accordance with ASHRAE, EPA, and industry standards.
Proper refrigerant piping can make the difference between a
reliable system and an inefficient, problematic system.

The primary concerns related to piping are refrigerant pressure
drop, a solid liquid feed to the expansion valves, continuous oil
return and properly sized refrigerant specialties.

Insulate the suction line to reduce excessive superheat build­up. Insulate the liquid line, where located in areas above
ambient temperature, to prevent loss of subcooling and
consequent liquid flashing.

The recommended source for refrigerant piping techniques and
sizing is the McQuay AG31-011 Refrigerant Piping Design
Guide.

Although conflicting piping recommendations can be found in
different sources, McQuay offers the following
recommendations for these controversial issues.

Use caution in sizing the liquid line in applications where the
evaporator is above the outdoor section. The weight of the
liquid refrigerant in the vertical column will decrease the
pressure at the top of the riser (approximately 0.5 psi per foot
of vertical rise) allowing some of the refrigerant to flash to a
gas. Adequate refrigerant subcooling is needed at the outdoor
section to prevent large volumes of refrigerant gas at the
expansion valve.

The piping systems should always extend above the highest
component in the refrigeration system before dropping down
to make the final refrigerant connections to components. This
practice will hinder the draining of condensed refrigerant to
the lower component when normal shutdown procedures do
not occur (such as a power failure).

Note: Do not run refrigerant lines underground.

1 Use type K or L clean copper tubing. Thoroughly clean or

braze all joints with high temperature solder. Make sure
nitrogen is flowing through the tubes while brazing to
minimize the formation of oxide contaminants.

2 Base piping sizes on temperature/pressure limitations as

recommended in the following paragraphs. Under no
circumstances should pipe size be based strictly upon coil
or condensing unit piping connection size.

3 To determine the minimum tonnage required to carry oil up

suction risers of various sizes, check the vertical suction
risers using Table 7.

4 Size the liquid line for a pressure drop not to exceed the

pressure equivalent of 2°F (1°C), 6 psi (41.4 kPa)
saturated temperature. The filter drier, solenoid, and

sight glass ship loose with each RFS unit.

The use of double risers for vertical gas risers is generally not
required and should be used only as a last resort to maintain
the minimum refrigerant flow to carry oil up the vertical risers.
Slightly downsizing the vertical riser is a preferable option to
providing double risers.

Slope the refrigerant lines 1" per 10 feet of horizontal run in
the direction of refrigerant flow to assist oil return.

Pressure drops in the refrigerant lines should be maintained at
or below the ASHRAE recommendations and line lengths
should be made as short as possible. Exceeding these

Table 7: Minimum Tonnage (R-410A) to Carry Oil Up
Suction Riser at 40°F Saturated Suction

Line size O.D. Minimum tonnage

1 1/8" 2.0

1 3/8" 3.5

1 5/8" 5.4

2 1/8" 11.2

2 5/8" 19.5

*3 1/8" 30.5

* McQuay’s largest suction connection is 2 5/8" and is generally sufficient.

recommendations will decrease performance and could impact
reliability.

30 McQuay IM 893-1

Piping Connections, RFS/RCS Units

Figure 34: Refrigerant Piping Connection Locations Example

DD

E

A

B

C

Mechanical Installation

F

EF

A

B

C

Table 8: 015D – 140D Connection Sizes and Locations

Piping Dimension

015D

030D

Dimension Component Circuit

A Liquid line #1/#2 Ckt.1 & 2 16.7" 12.9" 12.0" 13.5" 11.2" 20.8"
B HGBP line #1/#2 Ckt.1 & 2 24.0" 25.4" 25.9" 25.9" 28.1" 25.9"
C Suction line #1/#2 Ckt.1 & 2 32.7" 29.3" 29.4" 32.3" 32.3" 32.4"
D Liquid line #1/#2 Ckt.1 & 2 8.38" 8.38" 8.38" 8.38" 8.38" 8.38"
E HGBP line #1/#2 Ckt.1 & 2 6.02" 6.02" 6.02" 6.02" 6.02" 6.02"
F Suction line #1/#2 Ckt.1 & 2 6.62" 6.62" 6.62" 6.62" 6.62" 6.62"

-

025D

-

042D

045D

068D

070D

-

-

075D

Table 9: 015D – 140D Piping Diameter

Component Circuit

Liquid line #1/#2 Ckt.1 & 2 5/8" 5/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8"
HGBP line #1/#2 Ckt.1 & 2 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8"

Suction line #1/#2 Ckt.1 & 2 1 5/8" 1 5/8" 1 5/8" 1 5/8" 1 5/8" 1 5/8" 1 5/8" 1 5/8" 1 5/8" 1 5/8"

Component Circuit

Liquid line #1/#2 Ckt.1 & 2 7/8" 7/8" 7/8" 1 1/8" 1 1/8" 1 1/8" 1 1/8" 1 1/8" 1 1/8" 1 1/8" 1 1/8"
HGBP line #1/#2 Ckt.1& 2 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8" 7/8"

Suction line #1/#2 Ckt.1& 2 1 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8" 2 5/8"

015D 020D 025D 030D 035D 042D 045D 050D 060D 062D

068D 070D 075D 080D 090D 100D 105D 110 D 120D 125D 140D

080D

105D

Piping Diameter

110D

-

-

140D

Piping Diameter

McQuay IM 893-1 31

Mechanical Installation

Holding Charge

The RFS unit and RCS unit ship with a nitrogen holding
charge. At the time the unit was received, a visual inspection
of the unit piping should have been made to be sure no
breakage had occurred or that the fittings had not loosened. A
pressure test on the RCS units should indicate a positive
pressure in the unit. If no pressure is evident, the unit will have
to be leak tested and the leak repaired. This should be noted
and reported to the McQuay sales representative and freight
carrier if the loss is due to shipping damage.

WARNING

Before applying heat to remove brazed piping caps and plugs,
always vent piping to atmosphere. Failure to do so can cause
hazardous pressures, explosion, severe personal injuries, or
death.

RCS—Vent to atmosphere by opening gauge ports at the
compressors and liquid line shutoff valves. Make sure manual
valves are not back seated to shut off the gauge ports.

RFS—Vent to atmosphere by cutting off the process tubes on
the suction line caps.

The RFS unit does not have gauge ports for pressure
measurement. If no positive pressure is detected when cutting
off the process tubes and removing the tubing caps, the unit
should be leak tested as described below, after the
interconnecting piping has been brazed in place. This test will
also confirm the integrity of the field braze joints.

Leak Testing

In the case of loss of the nitrogen holding charge, the unit
should be checked for leaks prior to charging the complete
system. If the full charge was lost, leak testing can be done by
charging the refrigerant into the unit to build the pressure to
approximately 10 psig and adding sufficient dry nitrogen to
bring the pressure to a maximum of 125 psig. The unit should
then be leak tested with halide or electronic leak detector.
After making any necessary repair, the system should be

evacuated as described in the following paragraphs.

WARNING

Do not use oxygen or air to build up pressure. Explosion hazard
can cause severe personal injury or death.

Evacuation

After determining the unit is tight and there are no refrigerant
leaks, evacuate the system. Use a vacuum pump with a
pumping capacity of approximately 3 cu.ft./min. and the
ability to reduce the vacuum in the unit to at least 1 mm (1000
microns).

1 Connect a mercury manometer or an electronic or other

type of micron gauge to the unit at a point remote from the
vacuum pump. For readings below 1 millimeter, use an
electronic or other micron gauge.

2 Use the triple evacuation method, which is particularly

helpful if the vacuum pump is unable to obtain the desired
1 mm of vacuum. The system is first evacuated to
approximately 29" (740 mm) of mercury. Then add enough
refrigerant vapor to the system to bring the pressure up to 0
pounds (0 microns).

3 Evacuate the system again to 29" (740 mm) of vacuum.

Repeat his procedure three times. This method is most
effective by holding system pressure at 0 pounds
(0 microns) for a minimum of 1 hour between evacuations.
The first pulldown removes about 90% of the
noncondensables; the second removes about 90% of that
remaining from the first pulldown. After the third
pulldown, only 1/10 of 1% of noncondensables remains.

Table 12 on page 34 shows the relationship between pressure,
microns, atmospheres, and the boiling point of water.

CAUTION

To prevent liquid return and damage to the compressor on
systems with optional hot gas bypass, locate the bypass
solenoid valve on the RCS, not on the RFS unit.

CAUTION

Before replacing refrigerant sensors or protective devices, see
“Refrigerant Charge” on page 35 for an important warning to
prevent an abrupt loss of the entire charge.

CAUTION

To service liquid line components, the manual shutoff valve is
closed and refrigerant is pumped into the condenser. The
pounds of refrigerant in the system may exceed the capacity of
the condenser, depending on the amount of refrigerant in the
liquid lines between the RFS and RCS units. Suitable means of
containing the refrigerant is required.

32 McQuay IM 893-1

Mechanical Installation

Table 10: Approximate R-410A Refrigerant Charge per Circuit, 015D to 140D

Base charge

Unit size

015D 14 13 - - 2.8 - 8.7

020D 15 14 - - 2.8 - 8.7

025D 16 15 - - 2.8 - 8.7

030D 18 17 - - 2.8 - 8.7

035D-042D 19 18 - - 2.8 - 11.1

045D, 050D 20 19 24 23 4.1 4.5 16.3

060D, 062D 21 20 25 24 4.1 4.5 16.3

068D 22 21 26 25 4.1 4.5 16.3

070D, 075D 23 22 27 26 4.1 4.5 16.3

080D, 085D 24 23 28 27 4.7 5.3 26.1

090D 24 23 28 27 4.7 5.3 26.1

100D 24 23 28 27 5.3 6.7 26.1

105D 25 23 28 27 5.3 6.7 26.1

110D 35 34 39 38 5.3 6.7 30.3

120D 35 37 39 41 5.3 6.7 30.3

125D 38 37 42 41 - 6.7 30.3

130D 38 37 42 41 - 6.7 30.3

140D 38 40 42 44 - 6.7 30.3

* DX coil configuration (S = Standard, L = Large) is identified by the 8th digit of the RPS/RDT or RFS model number, found on the unit nameplate. For example,

DX = L for unit model number RFSO6ODLY.

Above values are for sealed core driers. Add 3.3#/ckt for replaceable core driers.

Blow through RPS RDT or draw through RPS

Circuit #1 Circuit #2 Circuit #1 Circuit #2

lbs per circuit (less DX coil)

DX coil charge

lbs per circuit per coil row

DX=S* DX=L*

Extra chargre

for HGRH

Table 11: Weight of Refrigerant in Copper Lines (Pounds per 100 feet of Type L Tubing)

Weight of refrigerant, lbs./100 feet

O.D. line size

3/8" 0.054 3.22 0.36 0.131

1/2" 0.100 5.97 0.67 0.243

5/8" 0.162 9.67 1.08 0.394

7/8" 0.336 20.06 2.24 0.816

1 1/8" 0.573 34.21 3.82 1.39

1 3/8" 0.872 52.06 5.81 2.11

1 5/8" 1.237 73.85 8.24 3.00

2 1/8" 2.147 128.18 14.30 5.22

2 5/8" 3.312 197.73 22.06 8.05

3 1/8" 4.728 282.26 31.49 11.49

3 5/8” 6.398 381.96 42.61 15.55

4 1/8" 8.313 496.29 55.36 20.20

Vol. per 100 ft.

in cubic feet

Liquid @110°F

(subcool to 15°F)

R-410A R-410A

Hot gas@127°F cond.

(superheat to 85°F)

Suction gas

(superheat to 10°F)

47°F set suction temp.

R-410A

McQuay IM 893-1 33

Mechanical Installation

Table 12: Pressure-Vacuum Equivalents

Absolute pressure above zero Vacuum below 1 atmosphere Approximate

Microns PSIA Mercury (mm) Mercury (in.)

0 0 760.00 29.921 — —

50 0.001 759.95 29,920 1/15,200 –50

100 0.002 759.90 29.920 1/7,600 –40

150 0.003 759.85 29.920 1/5,100 –33

200 0.004 759.80 29.910 1/3,800 –28

300 0.006 759.70 29.910 1/2,500 –21

500 0.009 759.50 29.900 1/1,520 –12

1,000 0.019 759.00 29.880 1/760 1

2000 0.039 758.00 29.840 1/380 15

4,000 0.078 756.00 29.760 1/189 29

6000 0.117 754.00 29.690 1/127 39

8,000 0.156 752.00 29.600 1/95 46

10,000 0.193 750.00 29.530 1/76 52

15,000 0.290 745.00 29.330 1/50 63

20,000 0.387 740.00 29.130 1/38 72

30,000 0.580 730.00 28.740 1/25 84

50,000 0.967 710.00 27.950 1/15 101

100,000 1.930 660.00 25.980 2/15 125

200,000 3.870 560.00 22.050 1/4 152

500,000 9.670 260.00 10.240 2/3 192

760,000 14.697 0 0 1 Atmosphere 212

fraction of

1 atmosphere

Boiling point

of H2O at each

pressure (

o

F)

Charging the System

RCS units are leak tested at the factory and shipped with a
nitrogen holding charge. If the holding charge has been lost
due to shipping damage, then contact the factory for
authorization and advice for repairing the leak and evacuating
the system.

1 After all refrigerant piping is complete and the system is

evacuated, it can be charged as described in the paragraphs
following. Connect the refrigerant drum to the gauge port
on the liquid shutoff valve and purge the charging line
between the refrigerant cylinder and the valve. Then open
the valve to the midposition.

2 If the system is under a vacuum, stand the refrigerant drum

with the connection up, open the drum, and break the
vacuum with refrigerant gas.

3 With a system gas pressure higher than the equivalent of a

freezing temperature, invert the charging cylinder and
elevate the drum above the condenser. With the drum in
this position and the valves open, liquid refrigerant flows
into the condenser. Approximately 75% of the total
requirement estimated for the unit can be charged in this
manner.

4 After 75% of the required charge enters the condenser,

reconnect the refrigerant drum and charging line to the
suction side of the system. Again, purge the connecting
line, stand the drum with the connection side up, and place
the service valve in the open position.

Note: Stamp the total operating charge per circuit on the unit

nameplate for future reference.

CAUTION

Adding refrigerant to the suction must always be done by
trained service personnel that are experienced with the risks
associated with liquid-related damage to the compressor.

Take special care to add refrigerant slowly enough to the
suction to prevent damage when first adding charge to the
suction. Adjust the charging tank hand valve extremely slow
such that only liquid leaves the tank but vapor enters the
compressor.

CAUTION

Units purchased for R-410A operation must be charged
only with R-410A.

Field mixing or changing of refrigerants can compromise
performance and damage equipment.

Table 13: Acceptable Refrigerant Oils

R-410A (polyester [POE] oils)

Note: Do not use mineral oils with R-410A.

Copeland ULtra 22 CC

Mobil EAL™ Arctic 22 CC

ICI EMKARATE RL™ 32CL

34 McQuay IM 893-1

Mechanical Installation

Refrigerant Charge

Each unit is designed for use with R-410A.The total charge per
circuit is the sum of the following four values:

• Condenser section charge, see Table 10 on page 33.

• Evaporator coil charge, see Table 10 on page 33.

• Charge for length of unit piping to the evaporator coil, see

Table 10 on page 33.

• Charge for length of interconnecting piping between the
RCS and RFS units, installed by field, see Table 11.

The exact charge for a one piece RPS/RDT is on the unit
nameplate.

Subcooling

When field charging the unit, use the following to properly
charge the unit:

• All compressors on each circuit operating at full capacity.

• Allowable liquid subcooling ranges are between 13°F to

20°F.

• Be sure to measure pressure and temperature at the same
location (liquid line service valve is recommended) when
finding/calculating subcooling. Compare the actual
temperature and pressures to the saturated liquid
temperature.

• Ambient temperature must be between 60°F and 105°F.

• Hot Gas Bypass NOT operating (only with option)

• SpeedTrol motors operating at 100% (only with option)

If any one of the above items is not followed, subcooling
readings will not be accurate and the potential exists for over or
undercharging of the refrigerant circuit.

Refrigeration Service Valves

The unit is shipped with all refrigeration service valves closed.
RDT, RPS and RCS units have the following:

All Units—One discharge valve is provided per refrigerant
circuit, located between the compressors and condenser.

All Units—One liquid valve is provided per refrigeration
circuit, located at end of condensing section opposite
condenser control box.

RFS units do not ship with service valves installed. Before
attempting to start the compressors, all refrigeration service
valves must be fully opened and backseated.

Unit Piping

Condensate Drain Connection

The unit is provided with a 1.5" male NPT condensate drain
connection. Refer to certified drawings for the exact location.
For proper drainage, level the unit and drain pan side to side
and install a P-trap

RPS units may have positive or negative pressure sections.
Use traps in both cases with extra care given to negative
pressure sections. In Figure 35, dimension “A” should be a
minimum of 8" (203 mm). As a conservative measure to
prevent the cabinet static pressure from blowing or drawing
the water out of the trap and causing air leakage, dimension A
should be two times the maximum static pressure encountered
in the coil section in inches w.c.

Draining condensate directly onto the roof may be acceptable;
refer to local codes. Provide a small drip pad of stone, mortar,
wood, or metal to protect the roof against possible damage.

If condensate is piped into the building drainage system, pitch
the drain line away from the unit a minimum of 1/8" per foot.
The drain line must penetrate the roof external to the unit.
Refer to local codes for additional requirements. Sealed drain
lines require venting to provide proper condensate flow.

Where the cooling coils have intermediate condensate pans on
the face of the evaporator coil, copper tubes near both ends of
the coil provide drainage to the main drain pan. Check that the
copper tubes are in place and open before the unit is put into
operation.

On units with staggered cooling coils, the upper drain pan
drains into the lower coil drain pan through a copper tube near
the center of the drain pan. Check that this tube is open before
putting the unit into operation and as a part of routine
maintenance.

Drain pans in any air conditioning unit have some moisture in
them, allowing micro-organisms to grow. Therefor,
periodically clean the drain pan to prevent this buildup from
plugging the drain and causing the drain pan to overflow.
Clean drain pans to prevent the spread of disease. Cleaning

should be performed by qualified personnel

WARNING

Drain pans must be cleaned periodically. Material in
uncleaned drain pans can cause disease.

Cleaning should be performed by qualified personnel.

.

McQuay IM 893-1 35

Mechanical Installation

S t a t i c P r e s s u r e " P "

( i n . w . o . )

D r a i n P a n

4 " ( 1 0 2 m m )

M i n i m u m

" A "

8 " ( 2 0 3 m m )

M i n . o r 2 x " P "

M i n i m i z e T h i s

D i m

e n s i o n

V i e w A

N o t e : D r a i n l i n e m u s t

n o t b e r u n h i g h e r

t h a n t h i s l e v e l

C o p p e r T u b e

( o n e e a c h e n d o f c o i l )

S e e V i e w " A "

R e t u r n

B y p a s s

S u p p l y

Figure 35: Condensate Drain Connection

Gas Piping

See the “Installation” section of the gas-fired furnace
installation manual, IM 684 or IM 685.

Valve and Piping)

Figure 37: Hot Water Valve Package

Hot Water Coil Piping

Hot water coils are provided without valves for field piping or
piped with three-way valves and actuator motors.

Note:

All coils have vents and drains factory installed.

Hot water coils are not normally recommended for use with
entering air temperatures below 40°F (4°C). No control system
can guarantee a 100% safeguard against coil freeze-up. Glycol
solutions or brines are the only freeze-safe media for operation
of water coils at low entering air temperature conditions.

When no factory piping or valve is included, the coil
connections are 1 5/8" ODM copper.

Note: With the factory piping and valve package, field piping

connections are the same NPT size as the valve with
female threading (see Figure 37 on page 36).

Refer to the certified drawings for the recommended piping
entrance locations. Seal all piping penetrations to prevent air
and water leakage.

Note: Factory-installed water valves and piping are bronze,

brass, and copper. Dissimilar metals within the
plumbing system can cause galvanic corrosion. To avoid
corrosion, provide proper di-electric fittings as well as
appropriate water treatment.

Figure 36: Hot Water Heat Section (Shown with Factory

CAUTION

Coil freeze possible. Can damage equipment.

Follow instructions for mixing antifreeze solution used. Some
products have higher freezing points in their natural state than
when mixed with water. The freezing of coils is not the
responsibility of McQuay International. Refer to “Winterizing
Water Coils” on page 112.

Steam Coil Piping

Steam coils are provided without valves for field piping, or
piped with two-way valves and actuator motors.

The steam heat coil is pitched at 1/8" (3 mm) per foot (305
mm) to provide positive condensate removal. When no factory
piping or valve is included, the coil connections are 2.5" male
NPT iron pipe.

With the factory piping and valve package, the field supply
connection is the same NPT size as the valve with female
threading (see Figure 39 on page 37).

Refer to the certified drawings for the recommended piping
entrance locations. All piping penetrations must be sealed to
prevent air and water leakage.

36 McQuay IM 893-1

Mechanical Installation

Note: The valve actuator spring returns to a stem up position

upon power failure. This allows full flow through the
coil.

Figure 38: Steam Heat Section (Shown with Factory Valve
and Piping)

Steam Piping Recommendations

1 Be certain that adequate piping flexibility is provided.

Stresses resulting from expansion of closely coupled piping
and coil arrangement can cause serious damage.

2 Do not reduce pipe size at the coil return connection. Carry

return connection size through the dirt pocket, making the
reduction at the branch leading to the trap.

3 Install vacuum breakers on all applications to prevent

retaining condensate in the coil. Generally, the vacuum
breaker is to be connected between the coil inlet and the
return main. However, if the system has a flooded return
main, the vacuum breaker to the atmosphere; the trap
design should allow venting of the large quantities of air.

4 Do not drain steam mains or takeoffs through coils. Drain

mains ahead of coils through a steam trap to the return line.

5 Do not attempt to lift condensate.

6 Pitch all supply and return steam piping down a minimum

of 1" (25 mm) per 10 feet (3 m) of direction of flow.

Steam Trap Recommendations

1 Size traps in accordance with manufacturers’

recommendations. Be certain that the required pressure
differential will always be available. Do not undersize.

2 Float and thermostatic or bucket traps are recommended for

low pressure steam. Use bucket traps on systems with on­off control only.

3 Locate traps at least 12" (305 mm) below the coil return

connection.

4 Always install strainers as close as possible to the inlet side

of the trap.

5 A single tap may generally be used for coils piped in

parallel, but an individual trap for each coil is preferred.

Steam Coil Freeze Conditions

If the air entering the steam coil is below 35°F (2°C), note the
following recommendations:

1 Supply 5 psi (34.5 kPa) steam to coils at all times.

2 Modulating valves are not recommended. Control should

be by means of face and bypass dampers.

3 As additional protection against freeze-up, install the tap

sufficiently far below the coil to provide an adequate
hydrostatic head to ensure removal of condensate during an
interruption on the steam pressure. Estimate 3 ft. (914 mm)
for each 1 psi (7 kPa) of trap differential required.

4 If the unit is to be operated in environments with possible

freezing temperatures, an optional freezestat is
recommended. See “Freeze Protection” on page 78 for
additional information.

Figure 39: Steam Valve Package

McQuay IM 893-1 37

Mechanical Installation

Airflow

Damper Assemblies

The optional damper assemblies described in this section
normally are ordered with factory-installed actuators and
linkages. The following sections describe operation and
linkage adjustment of the factory-installed option.

Economizer Dampers

Outside air intake is provided on both sides of the unit, and the
return air path is at the center of the damper set. As the single
actuator modulates the outside air dampers open, the return air
dampers close. Exhaust air exits the unit through the gravity
relief dampers provided at the end of the economizer section.

The damper is set so that the crankarm moves through a 90­degree angle to bring the economizer dampers from full open
to full close (see Figure 40). Access to the actuator and linkage
is from the filler section. Mechanical stops are placed in the
crankarm mounting bracket. Do not remove stops. Driving the
crankarm past the stops results in damage to the linkage or
damper. The unit ships with a shipping bolt securing the
linkage crankarm. Remove shipping bolt before use.

Figure 40: Damper Adjustment

38 McQuay IM 893-1

Note: For good airflow control, adjust linkages so damper

blades do not open beyond 70 degrees. Opening a
damper blade beyond 70 degrees has little effect on its
airflow.
Do not “overclose” low leak damper blades. The edge
seal should just lightly contact the adjoining blade. The
blades will lock up if they are closed so far the seal goes
over center.

Mechanical Installation

A i r f l o w

3 . 1 5 " ( 8 0 m m )
M a x . S t r o k e o f
D a m p e r L i n k a g e B a r

Intake Hood Damper (0% to 100% outside air)

Units requiring 100% outside air are provided with a rain hood
and dampers that can be controlled by a single actuator. The
actuator provides two-position control for opening the
dampers fully during unit operation and closing the dampers
during the off cycle. No unit mounted exhaust dampers are
provided.

Intake Hood Damper (0% to 30% outside air)

These dampers are intended to remain at a fixed position
during unit operation, providing fresh air quantities from 0 to
30% of the total system airflow, depending on the damper
setting. This setting is made at the linkage rod on units with
manually adjustable linkages.

On units provided with MicroTech III controls, the damper
position may be set at the controller keypad. During unit
operation, the two-position actuator drives the damper to the
position set on the keypad. During the off cycle, the damper is
automatically closed.

No unit-mounted exhaust dampers are provided with this
option.

Figure 41: Damper Linkage Bar Typical for All Sizes

Figure 42: Intake Hood Damper Adjustment

McQuay IM 893-1 39

Mechanical Installation

Unit duct opening

Unit base

9.76"

4.58"

Roof curb

Duct flanger

in roof curb

Flexible

connector

Ductwork

Cabinet Weather Protection

This unit ships from the factory with fully gasketed access
doors and cabinet caulking to provide weather resistant
operation. After the unit is set in place, inspect all door gaskets
for shipping damage and replace if necessary.

Protect the unit from overhead runoff from overhangs or other
such structures.

Recaulk field-assembled options such as external piping or
vestibules per the installation instructions provided with the

option.

CAUTION

Transportation, rigging, or maintenance can damage the unit’s
weather seal. Periodically inspect the unit for leakage. Standing
moisture can promote microbial growth, disease, or damage to
the equipment and building.

Installing Ductwork

On bottom-supply/bottom-return units, if a McQuay roof curb
is not used, installing contractor should make an airtight
connection by attaching field fabricated duct collars to the
bottom surface of either the roof curb’s duct flange or the
unit’s duct opening. Do not support the total weight of the duct
work from the unit or these duct flanges. See Figure 43.

Units with optional back return, side discharge, or end
discharge (on RFS units) all have duct collars provided. To

expose the discharge duct collars on a side discharge unit,
remove the plenum section access door and the door gasketing.

Use flexible connections between the unit and ductwork to
avoid transmission of vibration from the unit to the structure.

To minimize losses and sound transmission, design duct work
per ASHRAE and SMACNA recommendations.

Where return air ducts are not required, connect a sound
absorbing T or L section to the unit return to reduce noise

transmission to the occupied space.

WARNING

Mold can cause personal injury. Materials such as gypsum wall
board can promote mold growth when damp. Such materials
must be protected from moisture that can enter units during
maintenance or normal operation.

Ductwork exposed to outdoor conditions must be built in
accordance with ASHRAE and SMACNA recommendations

and local building codes

.

NOTICE

Installer must provide access in the ductwork for
plenum-mounted controls.
Once duct work is installed in units with side discharge, access
to plenum-mounted components is difficult.

Figure 43: Installing Duct Work

40 McQuay IM 893-1

Mechanical Installation

Static pressure

tubing

Installing Duct Static Pressure Sensor Taps

For all VAV units, duct static pressure taps must be field
installed and connected to the pressure sensors in the unit.
Sensor SPS1 is standard; additional sensor SPS2 is optional.
These sensors are located in the main control panel (see
“Control Panel” on page 9).

Carefully locate and install the duct static pressure sensing tap.
Improperly locating or installing the sensing tap causes
unsatisfactory operation of the entire variable air volume
system. Below are pressure tap location and installation
recommendations.The installation must comply with local
code requirements

1 Install a tee fitting with a leak-tight removable cap in each

tube near the sensor fitting. This facilitates connecting a
manometer or pressure gauge if testing is required.

2 Use different colored tubing for the duct pressure (HI) and

reference pressure (LO) taps, or tag the tubes. McQuay
recommends ¼" plastic tubing.

3 Locate the duct pressure (HI) tap near the end of a long

duct to ensure that all terminal box take-offs along the run
have adequate static pressure.

4 Locate the duct tap in a nonturbulent flow area of the duct.

Keep it several duct diameters away from take-off points,
bends, neckdowns, attenuators, vanes, or other
irregularities.

5 Use a static pressure tip (Dwyer A302 or equivalent) or the

bare end of the plastic tubing for the duct tap. (If the duct is
lined inside, use a static pressure tip device.)

6 Install the duct tap so that it senses only static pressure (not

velocity pressure). If a bare tube end is used, it must be
smooth, square (not cut at an angle) and perpendicular to
the airstream (see Figure 45).

7 Locate the reference pressure (LO) tap somewhere near the

duct pressure tap within the building (see Figure 44). If the
reference tap is not connected to the sensor, unsatisfactory
operation will result.

8 Route the tubes between the curb and the supply duct, and

feed them into the unit through the knockout in the bottom
of the control panel (see Figure 44). Connect the tubes to
appropriate barbed fittings in the control panel. (Fittings are
sized to accept ¼" plastic tubing.)

Figure 44: Static Pressure Tubing Entrance Location

Figure 45: Pressure Sensing Tubing Installation

Main Control Panel

"HI line"

"LO" line

Remote Sense Point

To Sensor
"HI" input

Tube
Clamps

Ductwork

(Remote Location)

Rubber
Grommet

SPS1

Roof

Tubing Extends
thru Approx. 1/8"

To Sensor
"LO" Input

Pressure Sensing

McQuay IM 893-1 41

Tubing

Mechanical Installation

Installing Building Static Pressure Sensor Taps

If a unit has direct building static pressure control capability,
you must field install and connect static pressure taps to
pressure sensor SPS2 in the unit. This sensor is located at the
bottom of the main control panel next to terminal block TB2
(see “Control Panel Locations” in the “Unit Description”
section of this manual).

Carefully locate and install the two static pressure sensing
taps. Improper location or installation of the sensor taps causes
unsatisfactory operation. Below are pressure tap location and
installation recommendations for both building envelope and
lab, or “space within a space” pressure control applications.

The installation must comply with local code requirements.

CAUTION

Fragile sensor fittings.

If you must remove tubing from a pressure sensor fitting, use
care. Do not use excessive force or wrench the tubing back and
forth to remove or the fitting can break off and damage sensor.

Building Pressurization Applications

1 Install a tee fitting with a leak-tight removable cap in each

tube near the sensor fitting. This facilitates connecting a
manometer or pressure gauge if testing is required.

2 Locate the building pressure (HI) tap in the area that

requires the closest control. Typically, this is a ground level
floor that has doors to the outside.

3 Locate the building tap so it is not influenced by any source

of moving air (velocity pressure). These sources may
include air diffusers or outside doors.

4 Route the building tap tube between the curb and the

supply duct and feed it into the unit through the knockout in
the bottom of the control panel (see Figure 44). Connect the
tube to the ¼-inch HI fitting for sensor SPS2.

5 Locate the reference pressure (LO) tap on the roof. Keep it

away from the condenser fans, walls, or anything else that
may cause air turbulence. Mount it high enough above the
roof so it is not affected by snow. Not connecting the

reference tap to the sensor results in unsatisfactory
operation.

6 Use an outdoor static pressure tip (Dwyer A306 or

equivalent) to minimize the adverse effects of wind. Place
some type of screen over the sensor to keep out insects.
Loosely packed cotton works well.

7 Route the outdoor tap tube out of the main control panel

through a small field-cut opening in the edge of the control
wiring raceway cover (see Figure 44 on page 41). Cut this
“mouse hole” in the vertical portion of the edge. Seal the
penetration to prevent water from entering. Connect tube to
the ¼-inch LO fitting for sensor SPS2.

Lab Pressurization Applications

1 Install a “T” fitting with a leak-tight removable cap in each

tube near the sensor fitting. This facilitates connecting a
manometer or pressure gauge if testing is required.

2 Use different colored tubing for the controlled space

pressure (HI) and reference pressure (LO) taps, or tag the
tubes.

3 Regardless whether the controlled space is positive or

negative with respect to its reference, locate the HI pressure
tap in the controlled space. (The setpoint can be set
between -0.2 and 0.2" w.c.)

4 Locate the reference pressure (LO) tap in the area

surrounding the controlled space. Not locating the
reference tap to the sensor results in unsatisfactory
operation.

5 Locate both taps so they are not influenced by any source

of moving air (velocity pressure). These sources may
include air diffusers or doors between the high and low
pressure areas.

6 Route the building tap tube between the curb and the

supply duct and feed it into the unit through the knockout in
the bottom of the control panel (see Figure 44).

7 Connect the tube to the ¼-inch HI fitting for sensor SPS2.

42 McQuay IM 893-1

Electrical Installation

Electric heat
control panel

Optional

disconnect

(DS3)

3" power

knockouts

Optional

disconnect (DS2)

3" power

knockouts

Main disconnect (DS1)

or power block (PB1)

R e m o v e L i f t i n g B r a c k e t
( I f L o c a t e d H e r e )
B e f o r e D r i l l i n g H o l e

M a i n
C o n t r o l
P a n e l

2 . 7 5 "
( 7 0 m m )

3 " ( 7 6 m m )

M a x

D i a .

1 6 "

( 4 0 6 m m )

Electrical Installation

Field Power Wiring

Wiring must comply with all applicable codes and ordinances.
The warranty is voided if wiring is not in accordance with
these specifications. An open fuse, tripped circuit breaker, or
Manual Motor Protector (MMP) indicates a short, ground, or
overload. Before replacing a fuse, circuit breaker, MMP, or
restarting a compressor or fan motor, identify the trouble and
correct.

According to the National Electrical Code, a disconnecting
means shall be located within sight of and readily accessible
from the air conditioning equipment. The unit can be ordered
with an optional factory mounted disconnect switch. This
switch is not fused. Power leads must be over-current
protected at the point of distribution. The maximum allowable
overcurrent protection (MROPD) appears on the unit
nameplate.

All RPS, RFS, and RDT Units

All units are provided with internal power wiring for single or
dual point power connection. The power block or an optional
disconnect switch is located within the main control panel.
Field power leads are brought into the unit through 3"
knockouts in the bottom of the main control panel. Refer to the
unit nameplate to determine the number of power connections.
See Figure 46 and Table 15 on page 45.

Figure 46: RPS/RDT and RFS Power Wiring Connections

Figure 47: Optional Side Power Wiring Entrance

WARNING

Hazardous voltage. Can cause severe injury or death.
Disconnect electric power before servicing equipment. More
than one disconnect may be required to de-energize the unit.

If the unit has a factory mounted disconnect switch, generally
the switch must be turned off to open the main control panel
door. However, the door can be opened without disconnecting
power by following the procedure covered on page 117. If this
is done, use caution since power is not removed from the unit
or the controller.

Note: To wire entry points, refer to certified drawings for

dimensions.

The preferred entrance for power cables is through the bottom
knockouts provided on the unit. If side entrance is the only

option, a drilling location is provided.

CAUTION

Wires are located in base rail. Move wires before drilling hole
through base rail.

The drilling dimensions must be followed exactly to prevent
damage to the control panel. The dimensions provided are the
only possible point of side entrance for the power cables.

McQuay IM 893-1 43

Electrical Installation

RCS Units

Field power wiring is connected from the main control panel in
the RFS unit to powerblock (PB4) or an optional disconnect
switch (DS4) located in the condenser control panel of the
RCS unit. Power leads enter the bottom left corner of the
condenser control panel through the conduit hubs shipped with
the unit. Refer to Figure 49 on page 45.

Figure 48: Typical Power Wire Entrance, Unit View—RPS 050D to 140D Shown (Actual Opening Shown on Submittal
Documents)

44 McQuay IM 893-1

All Units

The minimum circuit ampacity (wire sizing amps) is shown on
the unit nameplate. Refer to Table 15 on page 45 for the
recommended number of power wires.

Copper wire is required for all conductors. Size wires in
accordance with the ampacity tables in Article 310 of the
National Electrical Code. If long wires are required, it may be
necessary to increase the wire size to prevent excessive voltage
drop. Wires should be sized for a maximum of 3% voltage
drop. Supply voltage must not vary by more than 10% of
nameplate. Phase voltage imbalance must not exceed 2%.
(Calculate the average voltage of the three legs. The leg with
voltage deviating the farthest from the average value must not
be more than 2% away.) Contact the local power company for
correction of improper voltage or phase imbalance.

CAUTION

Provide proper line voltage and phase balance.
Improper line voltage or excessive phase imbalance constitutes
product abuse. It can cause severe damage to the unit's
electrical components.

Electrical Installation

Figure 49: RCS 050D to 140D Power Wiring Connections

A ground lug is provided in the control panel for each
disconnect or power block. Size grounding conductor in
accordance with Table 250-95 of the National Electrical Code.

In compliance with the National Electrical Code, an
electrically isolated 115V circuit is provided in the unit to
supply the factory mounted service receptacle outlet and
optional unit lights. This circuit is powered by a field
connected 15A, 115V power supply. Leads are brought into the
RFS and RPS units through a 7/8" knockout in the bottom of
the main control panel, near the power wire entry point.

Table 14: Multiple Point Power Connection Options

Number of

electrical

circuits

2 DS2 Supply and return fan

2 DS3 Electric heat Electric heat

3 DS3 Electric heat Electric heat

Disconnect

designation

DS1 Balance of unit Main control panel

DS1 Balance of unit Main control panel

DS2 Supply and return fan

DS1 Balance of unit Main control panel

Load

motors plus controls

motors plus controls

Location

(see Figure 9 on

page 9)

Main control panel

control panel

control panel

Main control panel

Table 15: Recommended 3-Phase Power Wiring to Ensure
Disconnects and Power Blocks Mate with Power Wiring

Wire

gauge

10 1 75 1 1/2 35

8 1 75 1 3/4 50
6 1 75 1 1 65
41 75 1 1 1/4 85
3 1 75 1 1 1/4 100
2 1 75 1 1 1/4 115

1 1 75 1 1 1/4 130
1/0 1 75 1 1 1/2 150
2/0 1 75 1 2 175
3/0 1 75 1 2 200
4/0 1 75 1 2 230

Qty./
pole

Insulation

rating

(°C)

No. of

conduits

Conduit

(trade size, in.)

For MCA

up to

(amps)

McQuay IM 893-1 45

Electrical Installation

Main control panel

24V field terminal

block (TB2)

Control wiring raceway
cover (remove for access
to harness from main control
box to unit-mounted
control devices)

Field Control Wiring

Roof Pak applied rooftop units are available with several
control arrangements which may require low voltage field
wiring. Detailed descriptions of various field control wiring
options and requirements are included in the “Field Wiring”
section of IM 919, MicroTech III Applied Rooftop Unit
Controller. Refer to the unit wiring diagrams for additional
installation information.

Wiring must comply with applicable codes and ordinances.
The warranty is voided if wiring is not in accordance with
these specifications.

RPS, RDT, and RFS Units

All field control wiring connections are made at the class II
terminal block TB2, which is located in the main control panel.
Field wiring connections to the 115 volt receptacle and lights
are made at terminal block TB7, which is also located in the
main control panel. Refer to Figure 50, Figure 51, and
“Control Panel” on page 9. Two 7/8" knockouts are provided
for wire entry.

RFS/RCS Units

The RCS unit receives 115V and 24V control circuit power and
a number of control signals from the RFS unit. Two 7/8"
knockouts are provided in the right side of the RCS control box.

Figure 51: Control Wiring Raceway

Figure 52: RFS and RCS Interconnecting Control Wiring

RFS Unit RCS Unit

Main

control

panel

TB4

Condenser

control

panel

PB4/DS4P

DS2

PB1/DS1

TB5 & TB6

24V

115V

Interconnecting wiring enters the RFS unit through 7/8"
knockouts in the bottom of the main control panel. The
interconnecting wiring is connected to TB4 in the RFS unit and
TB5 in the RCS unit. Refer to Figure 52. A 7/8" knockout is
also available in the end of the unit base as shown in Figure 50.

Note: If a single conduit containing 24V and 115V wiring is

run above the roofline between the RFS and RCS unit,
install the 24V wiring as an NEC Class I wiring system.

Figure 50: RDT, RFS, RPS Field Wiring Connections

WARNING

Electrical shock hazard. Can cause severe injury or death.
Connect only low voltage NEC Class II circuits to terminal
blocks TB2 and TB5.
Reinstall and secure all protective deadfront panels when the
wiring installation is complete.

46 McQuay IM 893-1

Preparing Unit for Operation

Hold-down
fasteners

Hold-down
fasteners

3 /8 " ± 1 /4 "
with fan running

Leveling
screw

Spring
mount

assembly

Cross

channel

Jam nut

Fan base

Preparing Unit for Operation

Spring Isolated Fans

WARNING

Moving machinery hazard. Can cause severe injury or death.
Before servicing equipment, disconnect power and lock off.
More than one disconnect may be required to de-energize unit.

Figure 53: RDT Spring Mount Hold Down Fasteners

Releasing Spring Mounts

The optional spring-mounted supply and return fans are locked
down for shipment. Hold-down fasteners are located at each
spring mount. Remove these fasteners before operating the
fans. Figure 55 shows a typical spring mount. Note that the
3/8" hold-down bolt securing the fan base to the unit cross
channel must be removed.

After removing the hold-down fasteners, rock the fan assembly
by hand to check for freedom of movement.

Figure 54: Fan Spring Mount Adjustment

Adjusting Spring Mounts

Figure 55: Spring Mount

To adjust spring mount compression, perform the following:

1 Loosen the .625-18 UNF hex nut (Figure 55).

2 Place additional weight on the fan sled frame and use a

lever to slightly compress the spring or raise the sled. This

will allow the bolt to turn freely.

3 Place one or two drops of oil on the threads if needed.

Note: The greatest friction that makes adjustment difficult,

comes from the surfaces of the top of the upper­rebound plate (Figure 55), both sides of the .615"
washer, and the underside of the sled. If friction is
occurring at these point, relieve the weight and oil
the friction surfaces.

4 Use a flat blade socket drive bit (1/2" drive handle

recommended) and make sure that when adjusting the

slotted bolt, that the upper-rebound plate also turns. The

slot is located just above the hex nut. This action allows the

bolt to push the compression plate (Figure 55) up or down

with the lease friction occurring between the .625" washer

and the underside of the channel.

Note: If the spring compresses to far, lift the sled before

turning. If the spring does not compress enough,
place weight on the sled corner, forcing it down
before turning.

5 Re-adjust the position of the lower-rebound plate so that

the sled has at least 3/4" travel and not more than 1.25" of

travel.

CAUTION

* Grossly out-of-adjustment thrust restraints can affect this dimension.

Recheck after thrust restraints are adjusted.

McQuay IM 893-1 47

Do no use impact tools for field spring mount adjustments as
damage to bits or to the bolt slot may occur.

WARNING

Moving machinery hazard. Can cause severe injury or death.
Start the fans for the first time according to the “Check, Test,
and Start Procedures” on page 92. If this is not done, equipment
damage, severe personal injury, or death can occur.

Preparing Unit for Operation

Fan base channel

Adjust up or down
or back and forth

Snubber neoprene

bumper

Snubber neoprene

bumper

.25 (6 mm) gap

(fan running)

Adjust in and out

Snubber restrainer angle

Relief Damper Tie-Down

Economizer sections with a 30" or 40" return fan have a relief
damper that is tied down for shipping. Remove the two
brackets and two screws before operation to allow free
movement of dampers. Access is from inside the economizer
section.

Adjustment of Seismic Restraints

Spring mounted supply air and return air fans may be ordered
with factory installed seismic restraints. Refer to Figure 56.
The system consists of four snubbers, one located next to each
spring isolator. These snubbers will allow free movement of
the fan assemblies during normal operation because normal
operation will not cause fan movements that exceed .25" (6
mm). However, they will restrain the fan assembly and limit
movement to .25" (6 mm) in any direction if an abnormal
condition were to occur.

The position the fan will assume during normal operation will
be determined by actual job site airflow and static pressure.
Therefore, for proper operation, the seismic restraints must be
field adjusted as part of the normal “Check, Test and Start”
procedure. When the fan is operating in a normal manner there
should be no contact between the snubber restrainer angle and
the snubber neoprene bumper. However, in a “seismic event,”
the snubber will limit movement of the spring mounted fan
assembly to .25" (6 mm) in any direction, thereby helping to
prevent the fan from being tossed about and damaged, or
causing damage.

When a seismic restraint is properly adjusted and the fan is
operating normally, the neoprene center bumper will be
centered within the 2" (51 mm) diameter hole in the restrainer
angle, and the restrainer angle will be centered vertically
between the flanges of the neoprene center bumper. This
results in .25" (6 mm) clearance in all directions. When the fan
is turned off the restrainer angle may come to rest on the
neoprene center bumper.

Figure 56: Cross Section of Seismic Restraint

The seismic restraint is adjustable in all directions. Vertical
slots in the restrainer angle and horizontal slots in the blower
base allow the restrainer angle to be adjusted up and down and
back and forth. The neoprene center bumper is mounted on a
slotted hole allowing its adjustment in and out.

Removing the neoprene center bumper bolt allows removal,
disassembly, and replacement of the neoprene components.

Adjusting Scroll Dampers

Two sets of scroll dampers are provided in the housing of the
twin 15" x 6" supply fan to allow control of air volume to each
fan wheel. At the factory, these dampers are fully closed,
unrestricting airflow. If fan paralleling occurs, correct it by
loosening the adjustment screw on top of the fan housing (see
Figure 57) and slightly lowering the rod until air distribution
between the fans is even.

48 McQuay IM 893-1

Figure 57: Scroll Damper Adjustment

Adjustment assembly

Scroll damper

Preparing Unit for Operation

Jam nut A

Nut B

Spring clip

Nut C

Jam nut A

Washer

Fan bulkhead

Thrust restraint angle

Fan housing frame

See Detail A

Detail A

Thrust restraint adjustment (with fan off)

1. Loosen jam nuts “A”.

2. Turn nut “C” until spring cup and washer contact thrust restraint
angle.

3. Turn nut “B” until spring is compressed by two turns of nut “B”.

4. Tighten jam nuts “A”.

Adjusting Supply Fan Thrust Restraints

Thrust restraints are provided when housed double-width fans
are mounted on springs. After the spring mounts are adjusted
for level operation when the fan is running, check the thrust
restraints. With the fan off, set the adjustment nuts so the
spring is slightly compressed against the angle bolted to the
fan housing frame. Refer to Figure 58. When the fan is turned
on, the fan moves back to a level position and the thrust
restraint springs compresses.

Figure 58: Thrust Restraint Adjustment

McQuay IM 893-1 49

Sequences of Operation

Sequences of Operation

The following sequences of operation are for a typical “C”
vintage applied rooftop unit equipped with MicroTech III, an
economizer, 4-compressor/4-stage cooling, 3 to 1 turn down
burner, variable frequency drives (VFD), a return air fan and
an external time clock. These sequences describe the ladder
wiring diagram logic in detail; refer to “Wiring Diagrams” on
page 55 as you read them. Note that your unit’s sequences of
operation may vary from those described here. Refer to the
wiring diagrams supplied with the unit for exact information.

For detailed description of operation information relating to
the MicroTech III controller's software, refer to the appropriate
operation manual (see Table 1 on page 3). These manuals
describe the various setpoints, parameters, operating states,
and control algorithms that affect rooftop unit operation.

Power-up

When primary power is connected to the unit, 115 V (ac)
power is fed through control circuit transformer T1 and control
circuit fuse F1C (line 166, Figure 63 on page 59) to
compressor crankcase heaters HTR-1, HTR-2, HTR-3 and
HTR-4 (lines 836 - 848, Figure 73 on page 69).

When system switch S1 (line 203, Figure 68 on page 64) is
closed, low voltage transformers T2 (line 203, Figure 68 on
page 64), T3 (line 251, Figure 69 on page 65) and T9 (line
802, not shown) energize, and 115 V (ac) power is supplied to
the following:

• The supply fan VFD (line 135-137, Figure 63 on page 59)

• M40A to energize the return fan VFD (line 147-149,

Figure 63 on page 59)

• Heating control panel (line 603, Figure 70 on page 66)

• Economizer actuator (lines 256-257)

Transformer T2 supplies 24 V (ac) power to terminals 24V and
COM on the main control board MCB (lines 207 and 208).
Transformer T2 supplies 24 V (ac) power to the following (see
Figure 62 on page 58 and Figure 63 on page 59):

• Switch S7 On-Auto-Off (line 217)

• Enthalpy sensor OAE (line 247)

• External time clock contacts (line 215)

• Airflow interlock switch PC7 (line 228)

• Dirty filter switches PC5 and PC6 (lines 242 and 247, not

shown)

• Gas furnace alarm relay R24 (line 225, not shown)

• Freezestat switch FS1 (line 244, hot water or steam heat

only, not shown)

• Smoke detectors SD1 and SD2 (line 237)

The time clock, S7 switch, and emergency shutdown terminals
(lines 217-222) control fan operation.

Note: Unit ships with factory installed jumpers between TB2

101 and 105 and between 101 and 106.

Fan Operation

When the main control board (MCB) commands the supply
and return fans to start, the unit enters the Startup operating
state. As a result, a 3-minute timer is set, output MCB-BO3
(line 307) energizes, and relay R26 energizes (line 306, not
shown).

After the 3-minute timer expires, the unit enters the Recirc
operating state. As a result, output MCB-BO1 energizes relay
R67 (line 401). This gives a start signal to supply fan drive
AFD10 (line 445). Four seconds after MCB-BO1 is energized,
output MCB-BO2 energizes relay R68 (line 404). This gives a
start signal to return fan drive AFD20 (line 445).

Within 120 seconds after the fans start, the controller expects
airflow switch PC7 (line 228) to close and thus energize binary
input MCB-BI6. (If MCB-BI6 does not energize, the controller
assumes the fans did not start. It then shuts down the unit and
generates an alarm.)

During the Recirc operating state, the outside air damper is
held closed. The controller does this by energizing output
MCB-BO5 (line 318). On VAV units, output MCB-BO12, the
VAV box output, is also de-energized (line 309) during the
Recirc state.

50 McQuay IM 893-1

Sequences of Operation

The supply fan adjustable frequency drive (AFD10) is
modulated to maintain the duct static pressure setpoint. When
energized, output MCB-BO14 (line 407) drives AFD10 toward
increased capacity; MCB-BO13 (line 405) drives it toward
decreased capacity. On VAV units or CAV units equipped with
return fan capacity control, the adjustable frequency drive
(AFD20) is modulated to maintain an acceptable building
static pressure (using either VaneTrol logic or direct
measurement of building pressure; see the appropriate OM for
more information). When energized, output MCB-BO16 (line

409) drives AFD20 toward increased capacity; MCB-BO15
(line 411) drives them toward decreased capacity.

Note: If the inverter bypass switch S4 (lines426 and 430) is in

the bypass position, MMP30 and MMP40 (line 132 and

144) protect the fans from excessive current draw. If
either the supply or return fan is drawing excessive
current, one of the MMPs triggers an auxiliary contacts
(line 426) and open the circuit, causing both fans to
stop.

Economizer Operation

Refer to Figure 69 on page 65. When the outdoor air is suitable
for free cooling, the switch in enthalpy sensor OAE is in
position “3” (line 248, Figure 69 on page 65) energizing
analog input AIX5. When AIX5 energizes, the economizer is
enabled. (Note: If selected from the keypad, the enthalpy
decision can be made based on outdoor temperature. In that
condition, if the outdoor air temperature is less than or equal to
the changeover set point, the economizer is enabled.) If
cooling is required, the economizer dampers (ACT3) are
modulated to maintain the discharge air temperature setpoint.
Analog input AIX5 drives the outdoor air dampers toward the
open and closed (line 256) position. If the outdoor air dampers
are wide open and more cooling is required, the dampers hold
their positions and mechanical cooling is activated (see
below).

When the outdoor air is not suitable for free cooling, the
switch in enthalpy sensor OAE is in position “1,”
de-energizing analog input AIX5. (Alternatively, the outdoor

air temperature is above the changeover setpoint plus the
economizer changeover differential). When the economizer is
disabled, the dampers are held at their minimum position.

Mechanical Cooling Operation

4-Compressor/4-Stage Unit

Refer to “Electric Heat Control” on page 68 and “RPS 60
Condensing Unit Control (With Scroll Compressors),
Continued” on page 71 as you read this sequence of operation.
In this configuration there are four equally sized compressors
and two cooling circuits. In the following description,
compressor #1 is lead. However, if Auto Lead/Lag Staging is
selected on the keypad, the lead compressor is the one in the
lead circuit with the least number of run hours.

When the unit disconnect is closed, 115 V (ac) power is
supplied directly from control transformer T1 to the
compressor crankcase heaters, HTR-1, 2, 3, and 4 (lines 836 ­848, 853) and motor protectors MP1, 2, 3, and 4 (lines 836 ­848, 854). This same 115 V (ac) source also goes through:

• System switch, S1 (line 203, Figure 68 on page 64)

• The optional phase voltage monitors, PVM1 and 2

(lines 203, 802, not shown)

• The optional ground fault relays, GFR1 and 2
(lines 203, 802, not shown)

Compressors are staged by 115 V (ac) power supplied to the
following:

• Frost protect FP1 to CCB1-BI8 (line 812, not shown)—
Optional when no hot gas bypass is ordered on the unit

• Frost protect FP2 to CCB2-BI8 (line 823, not shown)—
Optional when no hot gas bypass is ordered on the unit

• HP relay R1 to CCB1-BI7 (lines 812)

• HP relay R2 to CCB2-BI7 (lines 823)

• Compressor contactor status M1 to CCB1-BI9 (line 812)

• Compressor contactor status M2 to CCB2-BI9 (line 823)

• Compressor contactor status M3 to CCB1-BI10 (line 814)

McQuay IM 893-1 51

Sequences of Operation

Cross Circuit Loading

See line 812, Figure 74 on page 70. During a call for cooling,
if HP1 is satisfied, then DO1 closes. If MMP1 and MP1 are
satisfied, then M1 compressor contactor is energized to bring
on compressor 1 on refrigerant circuit 1 (line 708 - 710,
Figure 66 on page 62. The M1 auxiliary brings on:

• Required condenser fans (line 854)

• Liquid line drop solenoids (lines 855 and 856)

The drop solenoids are electrically energized by compressor
contactor auxiliary contacts. They open when the first
compressor turns ON and they close when the last compressor
turns OFF.

Compressor 2 (refrigerant circuit 2) is the 2nd stage of cooling
and is brought on in the same manner (line 823, Figure 74 on
page 70 and lines 708 - 710, Figure 66 on page 62).

Circuit 2 condenser fans and solenoids are controlled in the
same manner on lines 861 - 865).

The 3rd stage of cooling is controlled by DO2 (line 814) and
brings on compressor 3 if MMP3 and MP3 are satisfied.

The 4th stage of cooling is controlled by DO4 (lines 826) and
brings on compressor 3 if MMP3 and MP3 are satisfied.

Lead Circuit Loading

The loading and unloading process is similar except that both
compressors in the lead cooling circuit 1 energize before
energizing any compressors in lag circuit 2.

Heating

Gas Furnace, Super Modulating Burner (20:1
Turndown)

Refer to “HTD Gas Burner Schematic” on page 66 for a
sequence of operation.

52 McQuay IM 893-1

MicroTech III Controller Opera tion

3/23

System Summary

Advanced Menus
Alarm Lists

Unit State= Cooling

Clg Capacity=

25%

1/3McQuay AHU

Enter Password

Continue W/O Password

Version Information

Using the Keypad/Display

The keypad/display consists of a 5-line by 22 character
display, three keys and a “push and roll” navigation wheel.
There is an Alarm Button, Menu (Home) Button, and a Back
Button. The wheel is used to navigate between lines on a
screen (page) and to increase and decrease changeable values
when editing. Pushing the wheel acts as an Enter Button.

Figure 59: Keypad Controls

MicroTech III Controller Operation

The first line on each page includes the page title and the line
number to which the cursor is currently “pointing”. The line
numbers are X/Y to indicate line number X of a total of Y lines
for that page. The left most position of the title line includes an
“up” arrow to indicate there are pages “above” the currently
displayed items, a “down” arrow to indicate there are pages
“below” the currently displayed items or an “up/down” arrow
to indicate there are pages “above and below” the currently
displayed page.

Each line on a page can contain status only information or
include changeable data fields. When a line contains status
only information and the cursor is on that line all but the value
field of that line is highlighted meaning the text is white with a
black box around it. When the line contains a changeable value
and the cursor is at that line, the entire line is highlighted. Each
line on a page may also be defined as a “jump” line, meaning
pushing the navigation wheel will cause a “jump” to a new
page. An arrow is displayed to the far right of the line to
indicate it is a “jump” line and the entire line is highlighted
when the cursor is on that line.

The keypad/display Information is organized into five main
menus or menus groups; Alarm Lists Menu, System Summary
Menu, Standard Menus, Extended Menus and Advance
Menus.

Note – Only menus and items that are applicable to the specific

unit configuration are displayed.

The Alarm Lists Menu includes active alarm and alarm log
information. The System Summary Menu includes status
information indicating the current operating condition of the
unit. Standard Menus include basic menus and items required
to setup the unit for general operation. These include such
things are control mode, occupancy mode and heating and
cooling setpoints. Extended Menus include more advanced
items for “tuning” unit operation such as PI loop parameters
and time delays. Advanced Menus include the most advanced
items such as “unit configuration” parameters and service
related parameters. These generally do not needing changing

McQuay IM 893-1 53

or accessing unless there is a fundamental change to or a
problem with the unit operation.

Passwords

When the keypad/display is first accessed, the Home Key is
pressed, the Back Key is pressed multiple times, or if the
keypad/display has been idle for the Password Timeout timer
(default 10 minutes), the display will show a “main” page
where the user can enter a password or continue without
entering a password. The three password levels available are
Level 2, Level 4, and Level 6, with Level 2 having the highest
level of access. Entering the Level 6 password allows access to
the Alarm Lists Menu, System Summary Menu, and the
Standard Menus group. Entering the Level 4 password allows
similar access to Level 6 with the addition of the Extended
Menus group. Entering the Level 2 password allows similar
access to Level 4 with the addition of the Advanced Menus
group. The Level 2 password is 6363, the Level 4 is 2526, and
the Level 6 password is 5321. Continuing without entering one
of these three levels allows access only to the Alarm Lists
Menu and the System Summary Menu.

Note – Alarms can be acknowledged without entering a

password.

Figure 60: Password Main Page

The password field initially has a value **** where each *
represents an adjustable field. These values can be changed by
entering the Edit Mode described below.

MicroTech III Controller Operation

1/1

Enter Password

Enter Password

***

*

Figure 61: Password Entry Page

Entering an invalid password has the same effect as continuing
without entering a password.

Once a valid password has been entered, the controller allows
further changes and access without requiring the user to enter a
password until either the password timer expires or a different
password is entered. The default value for this password timer
is 10 minutes. It is changeable from 3 to 30 minutes via the
Timer Settings menu in the Extended Menus.

Navigation Mode

In the Navigation Mode, when a line on a page contains no
editable fields all but the value field of that line is highlighted
meaning the text is white with a black box around it. When the
line contains an editable value field the entire line is inverted
when the cursor is pointing to that line.

When the navigation wheel is turned clockwise, the cursor
moves to the next line (down) on the page. When the wheel is

turned counter-clockwise the cursor moves to the previous line
(up) on the page. The faster the wheel is turned the faster the
cursor moves.

When the Back Button is pressed the display reverts back to
the previously displayed page. If the Back button is repeated
pressed the display continues to revert one page back along the
current navigation path until the “main menu” is reached.

When the Menu (Home) Button is pressed the display reverts
to the “main page.”

When the Alarm Button is depressed, the Alarm Lists menu is
displayed.

Edit Mode

The Editing Mode is entered by pressing the navigation wheel
while the cursor is pointing to a line containing an editable
field. Once in the edit mode pressing the wheel again causes
the editable field to be highlighted. Turning the wheel
clockwise while the editable field is highlighted causes the
value to be increased. Turning the wheel counter-clockwise
while the editable field is highlighted causes the value to be
decreased. The faster the wheel is turned the faster the value is
increased or decreased. Pressing the wheel again cause the new
value to be saved and the keypad/display to leave the edit
mode and return to the navigation mode.

54 McQuay IM 893-1

Wiring Diagrams

Legend

ID Description Standard location

ACT3, 4 Actuator motor, economizer Economizer section
ACT5 Actuator motor, discharge

isolation damper

ACT6 Actuator motor, return air

isolation damper

ACT7 Actuator motor, heat face/

bypass

ACT8 Actuator motor, cool face/

Bypass

ACT10, 11Actuator motor, exhaust

dampers

ACT12 Actuator motor, enthalpy

wheel bypass damper

AFD10 Adjustable frequency drive,

supply fan

AFD11 Adjustable frequency drive,

evap cond. fans

AFD20 Adjustable frequency drive,

return/exhaust fan

AFD60 Adjust. freq. drive, energy

recovery wheel(s)
AS Airflow switch, burner blower Gas heat box
BM Burner blower motor Heat section, gas
C1–8 Power factor capacitors,

compressors
C10 Power factor capacitors,

supply fan
C11 Capacitors, Speedtrol, circuit #1Condenser bulkhead

C20 Power factor capacitors,

return fan
C21 Capacitors, Speedtrol, circuit #2Condenser bulkhead

CB10 Circuit breaker, supply fan Main control box
CB11 Circuit breaker, evaporative

condenser fan(s)
CB20 Circuit breaker, return/

exhaust fan
CB60 Circuit breaker, energy

recovery wheel
CCB1, 2 Compressor control boards,

refrig. circuits
CPC Circuit board, main, micro

controller
CPR Circuit board, expansion,

micro controller
CS1, 2 Control switches, refrig.

circuits
DAT Discharge air temperature

sensor
DFLH Design flow lefthand sensor Return section
DFRH Design flow righthand sensor Return section
DHL Duct hi-limit Main control box
DS1 Disconnect, total unit or cond/

heat
DS2 Disconnect, SAF/RAF/

controls
DS3 Disconnect, electric heat Electric heat box
DS4 Disconnect, condenser (RCS

Only)

Discharge section

Return section

Coil section, heat

Coil section, cool

Return section

Energy recovery section

AFD/supply fan section

Main/RCE control box

AFD/ret. ex. fan section

Energy recovery section

Condenser section

Supply Fan section

Return section

Main/cond. control box

Main control box

Main control box

Main control box

Main control box

Main control box

Main/cond. control box

Discharge section

Main control box

Main control box

RCS control box

Wiring Diagrams

ID Description Standard location

EAT Exhaust air temperature

sensor

EFT Entering fan air temperature

sensor
EHB1 Staged electric heat board Main control box
ERB1 Energy recovery board Main control box
ERM1 Energy recovery wheel motor #1Energy recovery section

ERM2 Energy recovery wheel motor #2Energy recovery section

F1A, B Fuse, control circuit

transformer (T1), primary
F1C Fuse, control circuit

transformer (T1), secondary
F2 Fuse, control circuit

transformer (T2), primary
F3 Fuse, burner blower motor Main control box
FB11, 12 Fuseblock, Speedtrol Main/cond. control box
FB31–40 Fuseblock, electric heat (top

bank)
FB41–50 Fuseblock, electric heat (bot.

bank)
FB65 Fuseblock, evap. cond. sump

heater
FD Flame detector Heat section, gas
FLC Fan limit control Heat section, gas
FP1, 2 Frost protection, refrig. circuits Coil section, cool
FS1, 2 Freezestat control Coil section, heat/cool
FSG Flame safeguard Gas heat box
GFR1, 2 Ground fault relay Main control box
GFS1, 2 Ground fault sensor Main control box
GFR4 Ground fault relay, condenser Condenser control box
GFS4 Ground fault sensor,

condenser
GRD Ground All control boxes
GV1 Gas valve, pilot Heat section, gas
GV2 Gas valve, main/safety Heat section, gas
GV3 Gas valve, redundant/safety Heat section, gas
GV4–8 Gas valve, main, hi turn down Heat section, gas
HL1–10 Hi-limits, pwr, elec heaters

(top bank)
HL11–20 Hi-limits, pwr, elec heaters

(bot. bank)
HL22 Hi-limits, gas heat (pre-filters) Supply fan section
HL23 Hi-limits, gas heat (final filters) Final filter section
HL31–40 Hi-limits, ctl. elec heaters (top

bank)
HL41–50 Hi-limits, ctl. elec heaters (bot.

bank)
HP1–4 Hi-pressure controls, refrig Main control box
HP5 Hi-pressure controls, gas Heat section, gas
HS1 Heat switch, electric heat

shutdown
HS3 Heat switch, electric heat

deadfront interlock
HTR1–6 Crankcase heaters On compressors
HUM1 Humidstat sensor Energy recovery section
IT Ignition transformer Gas heat box
LAT Leaving air temperature

sensor
LP1, 2 Low-pressure controls,

refrigeration

Energy recovery section

Supply fan section

Main control box

Main control box

Main control box

Electric heat box

Electric heat box

Main/cond. control box

Condenser control box

Heat section, electric

Heat section, electric

Heat section, electric

Heat section, electric

Main control box

Electric heat box

Energy recovery section

Main control box

McQuay IM 893-1 55

Wiring Diagrams

ID Description Standard location

LP5 Low-pressure control, gas Heat section, gas
LR10 Line Reactor, supply fan Inverter bypass box
LR20 Line reactor, return/exhaust

fan
LS1, 2 Limit switch, low fire, high fire Gas heat box
LT10–23 Light, cabinet sections Supply fan section
M1–8 Contactor, compressor Main/cond. control box
M10 Contactor, supply fan Main control box
M11–18 Contactor, condenser fans,

M20 Contactor, return fan Main control box
M21–28 Contactor, Condenser fans,

M29 Contactor, burner motor Gas heat box
M30 Contactor, reversing, invertor

M31–39 Contactor, electric heat (top

M40 Contactor, reversing, Invertor

M41–50 Contactor, electric heat (bot.

M60 Contactor, energy recovery

M64 Contactor, sump pump Main/cond. control box
M65 Contactor, sump heater Main/cond. control box
MCB Microprocessor circuit board Main control box
MJ Mechanical Jumper All control boxes
MMP1–8 Manual motor protector,

MMP10 Manual motor protector,

MMP11–18Manual motor protector, cond.

MMP20 Manual motor pr otector, r eturn

MMP21–28Manual motor protector, cond.

MMP30 Manual motor protector, invrtr.

MMP40 Manual motor protector, invrtr.

MMP51,
52, 53
MMP60 Manual motor protector,

MP1–6 Motor protector, compr.#1-6 On compressors
OAE Outside air enthalpy sensor Economizer section
OAT Outside air temperature

PB1, 2 Power block, power

PB3 Power block, power

PB4 Power block, power

PB9, 10 Power block, supply fan Junction box, split unit
PB11, 12 Power block, power

PB19, 20 Power block, return/exhaust

PC5 Pressure control, clogged filter Pre filter section

circuit #1

circuit #2

bypass, supply fan

bank)

Bypass, Return Fan

bank)

wheel

compressors

supply fan

fans, ckt#1

fan

fans, ckt#2

bypass, sup. fan

bypass, ret. fan

Manual motor protector,

exhaust fan(s)

energy recovery wheel

sensor

distribution

distribution, electric heat

distribution, condenser

distribution

fan

Inv. bypass/main cont. box

Main/cond. control box

Main/cond. control box

Inverter bypass box

Electric heat box

Inverter bypass box

Electric heat box

Main control box

Main/cond. control box

Main control box

Main/cond. control box

Main control box

Main/cond. control box

Inverter bypass box

Inverter bypass box

Prop exhaust box

Main control box

Economizer section

Main control box

Electric heat box

Condenser control box

Main control box

Junction box, split unit

ID Description Standard location

PC6 Pressure control, clogged final

filter
PC7 Pressure control, proof airflow Supply fan section
PC8 Pressure control, minimum

airflow
PC13, 23 Pressure control, Fantrol Condenser section
PM1 Phone modem Main control box
PS1, 2 Pumpdown switches, refrig

circuits
PS3 Pumpdown switch, RFS only Main control box
PVM1, 2 Phase voltage monitor Main control box
PVM4 Phase voltage monitor,

condenser
R1, 2 Relay, hi pressure reset Main/cond. control box
R3, 4 Relay, hi pressure delay Main/cond. control box
R5–8 Relay, safety, cool fail Main/cond. control box
R9, 10 Relay, compressor lockout Main/cond. control box
R11, 12 Relay, Speedtrol fan cycling Main/cond. control box
R20 Relay, Heat, gas/ steam/ hot

water
R21, 22 Relay, heat, gas (hi-turn

down)
R23 Relay, heat, gas & electric Gas/electric heat box
R24 Relay, heat alarm, gas Main control box
R25 Relay, heat, gas, start supply

fan inverter
R26 Relay, isol/exh. dampers,

open/close
R28 Relay, isolation damper,

safety
R29 Relay, remote fire alarm Main control box
R30 Relay, cool valve with face

bypass
R45 Relay, UV lights Main control box
R46, 47 Relay, supply fan inverter,

incr/decr
R48, 49 Relay, return fan inverter, incr/

decr
R58,59 Relay, heat wheel inverter,

incr/decr
R60 Relay, energy recovery wheel,

enable
R61 Relay, smoke detector,

discharge air
R62, 63, 65Relay, use on specials Main control box

R66 Relay, smoke detector, return

air
R67 Relay, supply fan, enable Main control box
R68 Relay, return fan, enable Main control box
R69 Relay, Inv. bypass VAV box

interlock
R70–79 Relay, use on specials Main control box
RAE Return air enthalpy sensor Return section
RAT Return air temperature sensor Return section
REC1 Receptacle, main box Main control box
REC2 Receptacle, condenser box Condenser control box
REC3 Receptacle, field power, 115V Discharge bulkhead
REC10–23Receptacle, cabinet sections Cabinet sections

S1 Switch, system on/off Main control box

Final filter section

Coil section, cool

Main/cond. control box

Condenser control box

Gas heat/main cont. box

Gas heat box

Main control box

Main control box

Main control box

Main control box

Main control box

Main control box

Main control box

Main control box

Main control box

Main control box

Main control box

56 McQuay IM 893-1

Wiring Diagrams

200/ H200

1. Field wiring

3. Shielded wire/cable

4. Main control box
terminals

5. Auxilliary box
terminals

6. Field terminals

7. Plug connector

8. Wire/harness number

General Notes

2. Factory wiring

9. Wire nut/ID

WN7

ID Description Standard location

S2 Switch, system on/off,

S3 Switch, furnace on/off Gas heat box
S4 Switch, inverter bypass, on/ off Main control box
S7 Switch, local on/auto/off to

S10–23 Switches, cabinet section

S40–45 Switches, door interlock, UV

SC11 Speed control, circuit #1 Condenser bulkhead
SC21 Speed control, circuit #2 Condenser bulkhead
SD1 Smoke detector, supply Discharge section
SD2 Smoke detector, return Return section
SPS1, 2 Static pressure sensors, duct/

SR1-3 Sequencing relays, electric

SV1, 2 Solenoid valves, liquid DX coils
T1 Transformer, main control

T2 Transformer, control input

T3 Transformer, control output

T4 Transformer, exh. damper

T5 Transformer, electric heat Electric heat box
T6 Transformer, dew point

T9 Transformer, refrig. circuit 24V Main control box
T11 Transformer, speedtrol (line/

TB1 Terminal block, internal Main control box
TB2 Terminal block, field Main control box
TB3 Terminal blocks, factory Main control box
TB4 Terminal block, RFS, field Main control box
TB5 Terminal block, RCS, field Condenser control box
TB6 Terminal block, RCS, factory Condenser control box
TB7 Terminal block, 115V

TB8 Terminal block, 115V conv.

TB11 Terminal block, heat Heat control box
TB25, 26,
27, 28
TC12,
13, 14
TD1, 2 Time delay, compressor

TD3, 4 Time delay, hi-pressure Main/cond. control box

condenser unit

controller

lights

lights

building

heat

(line/115 V (ac)

(115/24 V (ac)

(115/24 V (ac)

actuator (115/12 V (dc)

controller (115/24 V (ac)

240 V (ac)

convenience outlet, field

outlet, RCS, field

Terminal block, split unit
junction box
Temperature controls, Fantrol Condenser section

lockout

Condenser control box

Main control box

Cabinet sections

Cabinet sections

Main control box

Electric heat box

Main control box

Main control box

Main control box

Main control box

Main control box

Condenser section

Main control box

Condenser control box

Junction box, split unit

Main/cond. control box

ID Description Standard location

TD5–8 Time delay, part winding,

compr #1 - 4

TD10 Time delay, hi turn down

burner
TD11, 12 Time delay, low ambient Main/cond. control box
TR1, 2 Transducer, pressure Main control box
U1, 2 Unloaders, compressors On compressors
UV Ultra-violet light(s) Coil/discharge section
VM1 Valve motor #1, heating Gas heat box/ heat section
VM5 Valve motor #5, cooling Coil section, cool
VV1 Vent valve, gas heat Heat Section, Gas
ZNT1 Zone temp. sensor, setback Field installed

Main control box

Gas heat box

McQuay IM 893-1 57

Wiring Diagrams

Figure 62: VAV Fan Power (With SAF and RAF VFDs and Unit Powered Outlet/Light Circuit)

58 McQuay IM 893-1

Wiring Diagrams

Figure 63: VAV Fan Power (With SAF and RAF VFDs and Unit Powered Outlet/Light Circuit), Continued

McQuay IM 893-1 59

Wiring Diagrams

HSAF-1

HSAF-2

HSAF-3

ELECTRICAL

CIRCUIT #1

CUSTOMER

SUPPLIED

POWER

106

107

108

109

110

111

112

113

133

134

135

136

137

138

139

140

141

426

109

426

MTR

T3

T2

T1

T3B

T3A

T2B

T2A

T1B

T1A

L3B

L3A

L2B

L2A

L1B

L1A

T3

T2

L3

L2

T1L1

G

T3

T2

T1

L3

L2

L1

L3B

L3A

L2B

L2A

L1B

L1A

L3-3

L2-3

L1-3

SUPPLY-FAN

MMP10

M10

GLG1

DS1

PB11

PB11

111A

110A

109A

137A

138A

139A

137

138

139

(Schematic continues on next page.

)

Figure 64: Constant Volume Fan Power (SAF and RAF)

60 McQuay IM 893-1

Figure 65: Constant Volume Fan Power (SAF and RAF), Continued

/8.00

/4.00

/3.00

/2.00

/8.00

/2.00

HRAF-1

HRAF-2

HRAF-3

144

145

146

147

148

149

150

151

152

161

162

163

164

165

166

167

168

169

170

109

431

109

426

MTR

21

21

21

X3

X1X2

H4

H3

H2

H1

123

4

567

8

GRD

L3-1

L2-1

L1-1

T3

T2

T1

T3

T2

L3

L2

T1L1

T3B

T3A

T2B

T2A

T1B

T1A

L3B

L3A

L2B

L2A

L1B

L1A

L3-6

L2-6

L1-6

F1C

F1A

F1B

T1_N

T1

T1_115VAC

TB1A TB1A

PB11

RETURN-FAN

M20

MMP20

PB11

168A

168C

168B

164A

162A

164

162

149

150

151

(Schematic continues on the previous page.)

Wiring Diagrams

McQuay IM 893-1 61

Wiring Diagrams

Figure 66: RPS 75 Condensing Unit Power (With SpeedTrol and Scroll Compressors)

62 McQuay IM 893-1

Figure 67: VFD Control (SAF and RAF)

Wiring Diagrams

McQuay IM 893-1 63

Wiring Diagrams

Figure 68: VAV Control Inputs

64 McQuay IM 893-1

Figure 69: VAV Control Inputs, Continued

Wiring Diagrams

McQuay IM 893-1 65

Wiring Diagrams

T1 _N

6000 V

IT

115 VAC

R2 2

5 (L1)420 3

F

L2G

3k1

6k1

FD

FS G

8

6

9

710

4k1

2k2

5K 12K 11K 1

CO M NO

AS

R2 0

21

45

87

11

10

S3

T2_115 VAC /

268

HL22

SIG_ 1/ 427

PL19

1

PL 16

1

PL16

2

PL19

3

TB 3_174

10

PL 19

2

5 9

1

3

5

13 14

PL19

4

NB

R2 4

T1_N/ 16 8

PL19_5

13 14

S1 _1/201

M29

2 4

M29

1 3

GV4A

GV4B

GV1A

8

9

BM

4

6

SIG_ 2/ 42 7

PL 18

6

T1 N/ 168

LP 5

R W

HP 5

R B

optional

T3 T2

CO M NO

FA N

LIMI T

FL C

T7

T8

CO M NO

X7

EXP B

M

X2

X3

X1

T3_24 VAC

M

R2 2

5 9

GR D

PL18

3

M

X4

R2 4

5 9

PL18

4

PL18

5

+

VM 1

-

T2

T1

T3 _N

R2 0

13 14

DO 1

203E

C1 DO 1

T2_115 VAC /

268

T1_N/ 168

EXP B

168A

PL18_8

HL23

PL19

9

1212

LS 1

LS 2

PL 196PL 19

7

PL19

8

CO M NO

CO M NO

DO 2

EXP B

GV1B

PL18

2

PL18

1

temp sensor

Ty pical Sequence of Operation

When 120V power is furnished through the system on/o switch (S1), through the burner on/o switch (S3), and through the high limit control (FLC), terminal #6 on the  ame

safeguard (FSG) is po wered on a call for heat. Whenever power is restored to the ame safeguard, the ame safeguard will go through a 10 second initiation period before the

prepurge period will begin. The burner air control valve will be at minimum position during o cycles. Upon a call for heat or any other time that a prepurge cycle will occur, the

ll llb d h f h dh d h fl 

Figure 70: HTD Gas Burner Schematic

66 McQuay IM 893-1

Figure 71: HTD Gas Burner Schematic, Continued

6000 V

IT

115 VAC

5 (L1)420 3

F

L2G

3k1

6k1

FD

6

710

5K 12K 11K 1

CO M NO

AS

NB

R2 4

T1_N/ 16 8

PL19_5

13 14

M29

1 3

GV4B

4

6

X2

X3

X1

R2 2

5 9

GR D

M

X4

R2 4

5 9

R2 0

13 14

DO 1

203E

C1 DO 1

T2_115 VAC /

268

T1_N/ 168

EXP B

168A

PL18_8

LS 1

LS 2

6

PL 19

7

PL19

8

CO M NO

CO M NO

Ty pical Sequence of Operation

When 120V power is furnished through the system on/o switch (S1), through the burner on/o switch (S3), and through the high limit control (FLC), terminal #6 on the  ame

safeguard (FSG) is po wered on a call for heat. Whenever power is restored to the ame safeguard, the ame safeguard will go through a 10 second initiation period before the

prepurge period will begin. The burner air control valve will be at minimum position during o cycles. Upon a call for heat or any other time that a prepurge cycle will occur, the

air control valve will be repositioned to the maximum position for the prepurge and then returned to the minimum position for low re start.

Upon a call for heat, the controller will close (EMB-D O 1) energizing R20, closing it’s N/O contact and energize terminal # 6 on the FSG. The FSG then energizes its terminal #4,

which powers the burner combustion air blower motor (BM) and starts the prepurge cycle. The call for heat will al so initiate the controller to reposition the burner air valve to its

maxi mum open position for prepurge. When the actuator reaches the full open position, switch (LS2) is 'made' which will provide a digital input to the controller (EMB -DI X3).

This digital input will initiate a 20 second (adjustable) timing period in the controller. At the completion of the timing period, the controller will si gnal the actuator to drive to its

minimum (low re) position. At the completion of the FSG prepurge cycle the valve will be at the minimum open position and the minimum position switch (LS1) will be 'made',

providing a digital input to the controller (EMB -DI X2). When the burner air valve is at it minimum position and the low position switch (LS1) is made, the controller will close

the digital output (EMB-DO 2) allo wing the combination gas valve(s) (GV1) to be energi zed upon completion of the FSG prepurge cycle.

After completion of the FSG prepurge period there will be a 10 second trial for ignition during whic h terminal #8 (combination gas valve - GV1) and te rminal #10 (ignition

transformer - IT) will be energized. If  ame is being detected through the ame rod (FD) at the completion of the 10 second trial for ignition period, terminal #10 (ignition

transformer - IT) will be de-energized and terminal #9 (main gas valves - GV4) will be energized and the control system will be allowed to control the ring rate once the heating

stage timer (default 5 minutes) has passed. After the ame has lit and been proven and the heating stage time has passed, the controller will modulate (V M1), to the required ring

rate. In the event the ame fails to ignite or the ame safeguard fails to detect its ame within 10 seconds, terminals #4, 8, 9, and 10 will be de-energized, thus de-energizi ng the

burner. The FSG would then lockout and would require manual resetting. If the FSG goes into lockoput, terminal 3 on the FSG will be energized and will energize R24, providing

a digital input to the controller (EMB-DI X2If an atte mpt is made to restart the burner by resetting the FSG or if an automatic restart is initiated after ame failure the earlier

described prepurge cycle wit h the wide open air valve will be repeated. If the unit overheats, the high limit control (FLC) will cycle the burner, limiting furnace temperature to the

limit control set point. The ame safeguard contains 'LEDS' (l ower left corner) that will gl ow to indicate operation.

Wiring Diagrams

McQuay IM 893-1 67

Wiring Diagrams

Figure 72: Electric Heat Control

68 McQuay IM 893-1

Figure 73: Electric Heat Control (Continued)

Wiring Diagrams

McQuay IM 893-1 69

Wiring Diagrams

Figure 74: RPS 60 Condensing Unit Control (With Scroll Compressors)

70 McQuay IM 893-1

Figure 74: RPS 60 Condensing Unit Control (With Scroll Compressors), Continued

Wiring Diagrams

McQuay IM 893-1 71

Wiring Diagrams

401A

404A

426C426B426A

431A

TB2

42

TB2

45

2

R68

10

2

R67

10

R68

3

404

1

R67

3

401

1

M20

A2A1

M10

A2A1

jprs

24V SRC

MCB

2 2NO

BO2

RETURN FAN

207

jprs

24V SRC

MCB

1 1NO

BO1

SUPPLY FAN

207

SRC 9-16

MCB

207

11(31)

MMP10

12(32)

11(31)

MMP20

12(32)

TO MOTHERBOARD

WIRED INTERNAL

SOURCE 9-16

T3_COM

/3.11

T3_24V

/3.11

115VAC_GF/1

T1_N

/1.68

REC1

FIELD SUPPLIED 115V/60/1

1003B1003A

1004B

1005B1005A

N

TB7

G

TB7

H

TB7

REC1

CP SL

GRD

SLCP

PL32

1

S11

PL31

1

S10

G1004

2

PL32

G1012

N

G

REC11

H

31

LT11

BLK WHT

w

2

PL31

G1009

N

G

REC10

H

30

LT1 0

BLK WHT

w

FIELD SUPPLIED 115V/60/1

H1010-2H1010-1

H775

H776

H775

H1006-2

H1006-1

H776

H775

H775

Figure 75: CV Fan Control (SAF and RAF)

Figure 76: Light and Receptacle Power (Field Power)

72 McQuay IM 893-1

Unit Options

3 5

( 1 . 5 )

4 0

( 4 . 5 )

4 5
( 7 )

5 0

( 1 0 )

6 0

( 1 5 . 5 )

6 5

( 1 8 . 5 )

7 0

( 2 1 )

7 5

( 2 4 )

8 0

( 2 6 . 5 )

8 5

( 2 9 . 5 )

9 0

( 3 2 )

9 5

( 3 5 )

1 0 0

( 3 8 )

1 0 5

( 4 0 . 5 )

5 5

( 1 3 )

1 2

1 4

1 6

1 8

2 0

2 2

2 4

2 6

3 0

3 2

3 4

3 6

3 8

4 0

4 2

4 4

4 6

2 8

E N T H A L P Y  B T U P E R P O U N D D R Y A I R

C

B

A

D

D

C

B

A

0 . 5 0

0 . 4 0

0 . 3 0

0 . 2 0

0 . 1 0

0 . 6 0

0 . 7 0

0 . 8 0

0 . 9 0

R E L A T I V E

H U M I D I T Y

3 5

( 1 . 5 )

4 0

( 4 . 5 )

4 5

( 7 )

5 0

( 1 0 )

5 5

( 1 3 )

6 0

( 1 5 . 5 )

6 5

( 1 8 . 5 )

7 0

( 2 1 )

7 5

( 2 4 )

8 0

( 2 6 . 5 )

8 5

( 2 9 . 5 )

9 0

( 3 2 )

9 5

( 3 5 )

1 0 0

( 3 8 )

1 0 5

( 4

0 . 5 )

Unit Options

Control Actuators

The actuators are controlled by an analog signal from the unit
controller. Damper actuators utilize a 0-10 V (dc) analog
signal while modulating heating/cooling valve actuators utilize

Figure 77: Control Actuators Wiring Diagram

a 2-10 V (dc) signal. Spring-return actuators are used for the 0

- 30% outdoor air and economizer dampers. The mixing
dampers are normally closed to the outside air.

Enthalpy Control

Figure 78: Enthalpy Control Settings

Outside Air Enthalpy Control (OAE)

Units with MicroTech III control and an economizer come
standard with an electromechanical enthalpy control device
(OAE) that senses both the humidity and temperature of the
outside air entering the unit. This device has an enthalpy scale
marked A through D. Table 16 shows the control points at 50%
RH for settings A through D. Figure 78 shows this scale on a
psychrometric chart. When the outside air conditions exceed
the setting of the device, the outside air dampers are positioned
to the minimum outside air intake position by the MicroTech

III controller.

Table 16: Enthalpy Control Settings

Control curve Control point temperature at 50% RH

A73°F (23°C)
B70°F (21°C)
C 67°F (19*C)
D63°F (17°C)

McQuay IM 893-1 73

Unit Options

Differential Enthalpy Control (OAE/RAE)

An optional electric differential enthalpy control arrangement
(OAE/RAE) is available on units with MicroTech III control.
In this configuration a solid-state humidity and temperature
sensing device is located in both the return (RAE) and outside
intake (OAE) airstreams. This OAE device has the same A
through D scale as the device described above. However, with
the OAE/RAE arrangement the switch on, OAE must be set all
the way past the D setting. With this done, the MicroTech III
controller adjusts the return and outside air dampers to use the
airstream with the lowest enthalpy.

Ground Fault Protection

The ground fault protection is designed to protect motors from
destructive arcing ground faults. The system consists of a
ground fault relay and a ground fault current sensor. The
ground fault relay employs solid state circuits that will
instantly trip and open a set of relay contacts in the 115-volt
control circuit to shut the unit down whenever a ground fault

condition exists. The ground fault relay is self powered. The
ground fault sensor is a current transformer type of device
located on the load side of the power block through which the
power wires of all phases are run.

Phase Voltage Monitor

The phase voltage monitor (see page 117) protects against high
voltage, phase imbalance, and phase loss (single phasing)
when any one of three line voltages drops to 74% or less of
setting. This device also protects against phase reversal when
improper phase sequence is applied to equipment, and low
voltage (brownout) when all three line voltages drop to 90% or
less of setting. An indicator run light is ON when all phase
voltages are within specified limits. The phase voltage monitor
is located on the load side of the power block with a set of
contacts wired to the 115-volt control circuit to shut the unit
down whenever the phase voltages are outside the specified
limits.

74 McQuay IM 893-1

Modulating Hot Gas Reheat

In the dehumidification mode, mechanical cooling is used to
cool air low enough to lower the moisture content of the air
and then reheated to comfort conditions.

Figure 79: Dual 2-Way Valve Refrigeration Schematic

Unit Options

Figure 80: Ideal for Neutral Air Ventilation Control

McQuay IM 893-1 75

Dehumidification Initiation

An analog sensor is mounted in the return duct, the space, or
outdoors to sense Relative Humidity. The location is selected
by setting the Sensor Location value on the keypad to Return,
Space, or OAT. OAT can only be selected for units with DAT
control. Dehumidification is disabled when the unit is in either
the Heating or Minimum DAT state. When Dehumidification
is enabled, Dehumidification operation is initiated when
Humidity Control is set to either Relative Humidity or Dew
Point and that value rises above the appropriate setpoint by
more than half its deadband. Economizer operation is disabled
in the Dehumidification mode so the unit immediately
transitions to Cooling if Dehumidification is initiated in
Economizer state.

Unit Options

Dehumidification Termination

Dehumidification is terminated if the selected variable,
Relative Humidity or Dew Point, drops below the appropriate
humidity setpoint by more than half its deadband.
Dehumidification is also terminated if cooling is disabled for
any reason or the unit enters either the Heating or Minimum
DAT state. For units with compressors, the number of cooling
stages is reduced by one and control reverts to normal control
when dehumidification is terminated in the Cooling state.
Another compressor stage change could then occur after one
Cooling Stage Time has elapsed.

Control & Arrangement

In conjunction with dehumidification, MHGRH is used to raise
the temperature of the cooled air to a desirable value. MHGRH
is comprised of a parallel coil arrangement, with both the
condenser and reheat coils of the micro channel type, dual
reheat valves (which operate in concert with one another) and
a check valve. MHGRH components will always be installed
in circuit #2.

During Dehumidification control w/ modulating Hot Gas
Reheat (MHGRH) an analog signal (0-10Vdc) is controlled as
described below.

• A PI Loop is used to control the HGRH valves to maintain
the Discharge Air Temperature from the reheat coil.

• Compressor staging during reheat (or dehumidification) will
be controlled by the Leaving DX Coil Temperature. For
increased dehumidification during reheat, the standard
default compressor staging range is 45 - 52°F.

• When dehumidification is active in the Cooling state, the
reheat set point equals the DAT Cooling Setpoint. For DAT
units, this is the normal DAT set point resulting from any
reset. For Zone Control units, this set point is the result of a
PI Loop based on the Control Temperature.

• Communication with the reheat control valves is
accomplished by providing a 0-10Vdc signal to a pair of
interface boards which in turn supply the control signal to
the reheat valves (step type).

• In the Fan Only state, no sensible cooling is required, but the
dehumidification mode will still be enabled if the dew point
or humidity sensor is not satisfied. In this case the reheat set
point varies from a maximum value (default 65°F) when the
Control Temperature is at or below the heating changeover
setpoint to a minimum value (default 55°F) when the

Control Temperature is at or above the cooling changeover
setpoint.

• Lead/Lag Arrangement w/ MHGRH (when applicable)

- Alternate staging with circuit #1 as lead will be the stan­dard default arrangement.

- During cooling mode, circuit #1 will lead and load up
before starting circuit #2.

- During reheat mode, circuit #2 will lead and load up before
starting circuit #1.

- For reheat operation, compressor(s) in circuit #2 must be
active. If the unit is operating in the cooling mode when a
call for dehumidification/reheat arises,circuit #2 will
become the lead and the controller will bring on an addi­tional stage of coolingfor dehumidification. If any com­pressors in circuit #1 are operating at this moment they
will be switched over to compressors in circuit #2. Dehu­midification operation is disabled if circuit #2 is disabled
for any reason.

• In the reheat mode, the minimum position for the reheat
valves is 10% (1.0 Vdc). The controller will modulate the
reheat valves from this starting position.

• Reheat valve(s) must be at 0% (0 Vdc) position before
starting the first compressor in the reheat circuit to prevent
pressure spikes.

• Upon termination of dehumidification (reheat), the
maximum ramp down or decay rate of the reheat control
valves shall be 1% per sec (or 0.1V per sec).

• Upon termination of dehumidification (reheat), staging of
compressor(s) is delayed for 1 minute after reheat capacity =
0% (0Vdc).

• Every 24 hours, the reheat control valves will be driven to
their maximum position (10Vdc) and then returned to their
normal operating position (0Vdc). If unit is operating in
cooling or dehumidification (reheat) at the prescribed time it
will be deferred to the next time.

•

Dehumidification status can now be found under the MTIII
main system menu. Reheat capacity (valve position) can also
be found under the main system menu, display based on
percentage (0-100%).

76 McQuay IM 893-1

Unit Options

Hot-Gas Bypass (HGBP)

Hot-gas bypass (Figure 81) provides protection against low
suction and frosting. It also helps keep the unit operating at
light load without excessive cycling.

The system consists of a pressure regulating valve that starts to
modulate open at 100 psig (32°F). The valve is fully open at
90 psig (26°F). The factory settings can be modified in the
field as the valve is adjustable.

Adjustments are made by turning the adjustment screw
clockwise (to increase valve setpoint) or counter clockwise.
The average psi change per turn is 16 psi.

Figure 81: Hot-Gas Bypass (HGBP) Diagram

Note: The regulating valve opening point can be determined

by slowly reducing the system load or reducing the
required discharge air temperature setting while
observing the suction pressure. When the bypass valve
starts to open, the refrigerant line on the evaporator side
of the valve will begin to feel warm as your hand
approaches the copper tube.

CAUTION

Do not touch the hot gas line during valve checkout. Place your
hand near it to feel the heat, or use gloves. The hot gas line can
become hot enough in a short time to cause personal injury.

External Time Clock

You can use an external time clock as an alternative to (or in
addition to) the MicroTech III controller’s internal scheduling
function. The external timing mechanism is set up to open and
close the circuit between field terminals 101 and 102. When
the circuit is open, power is not supplied to binary input
MCB-BI1. This is the normal condition where the controller
follows the programmable internal schedule. When the circuit
is closed, power is fed to BI1. The MicroTech III controller
responds by placing the unit in the occupied mode, overriding
any set internal schedule.

For more information, see the “Digital Inputs” section of IM
919, “MicroTech III Applied Rooftop Unit Controller.”

Smoke and Fire Protection

McQuay optionally offers factory installed outdoor air, return
air, and exhaust air dampers as well as smoke detectors in the
supply and return air openings, complete with wiring and
control. These components often are used in the building’s
smoke, fume, and fire protection systems. However, due to the
wide variation in building design and ambient operating
conditions into which our units are applied, we do not
represent or warrant that our products will be fit and sufficient
for smoke, fume, and fire control purposes. The owner and a
fully qualified building designer are responsible for meeting
all local and NFPA building code requirements with respect to

smoke, fume, and fire control.

WARNING

Improper smoke, fire, or fume air handling can result in
severe personal injury or death.

McQuay IM 893-1 77

Unit Options

Smoke Detectors

Field installed smoke detectors in the return air ductwork or
the supply air ductwork can be coordinated with the units
operation through the unit controller's binary input, D14. This
input in wired to TB2 and the supply air smoke detector can be
wired between terminals 103 and 104 and the return air smoke
detector can be wired between terminals 104 and 105. The T2
transformer supplies 24 V (ac) across each of these terminals
and a dry set of contacts can be wired to these terminals
respectively. This and additional wiring information can be
seen on the input wiring schematics at line number 220.

Figure 82: Smoke Detector Schematic

Factory installed smoke detectors have similar wiring and the
control sequence is as follows:

When smoke is detected by either sensor, the normally closed
sensor contacts open. This removes power from binary input
B18 on the main control board.

The Microtech III controller responds by shutting down the
unit. The controller is placed in the Alarm Off state and cannot
be restarted until the alarm is manually cleared. Refer to the
operation manual supplied with the unit for information on
clearing alarms.

The smoke detectors must be reset manually once they have
been tripped. Power must be cycled to the smoke detector to
reset.

Emergency Shutdown

The terminals 105 & 106 on TB2 can be used for any field
supplied component that requires a unit emergency shutdown.
When these terminals are used, the factory installed jumper
must be removed.

Freeze Protection

An optional freezestat is available on units with MicroTech III
control that have hot water, chilled water, or steam heating
coils. The sensing element is located on the downstream side
of the heating coil in the heating section of the unit. If the
freezestat detects a freezing condition and closes, the
MicroTech III controller takes different actions, depending on
whether the fans are on or off. The freezestat is an auto reset

type of control; however, the controller alarm that it causes is
manually reset if the fan is on and auto reset if the fan is off.

Fan On Operation

If the freezestat detects a freezing condition while the fan is
on, the MicroTech III controller shuts down the fans, closes the
outdoor air dampers, opens the heating valve, and sets a 10­minute timer. The MicroTech III controller’s active alarm is
“Freeze Fault.”

When the 10-minute timer expires, the controller begins
checking the freezestat again. If the freezestat is open, the
heating valve closes. If the freezestat closes again, the heating
valve opens, and the 10-minute timer resets.

The unit remains shut down until the “Freeze Fail” alarm is
manually cleared. Refer to the operation manual supplied with
the unit for information on clearing alarms (OM138 or
OM137).

Fan Off Operation

If the freezestat detects a freezing condition while the fan is
off, the MicroTech III controller opens the heating valve and
sets a 10-minute timer. The MicroTech III controller’s active
alarm is “Freeze Problem.”

When the 10-minute timer expires, the controller begins
checking the freezestat again. If the freezestat is open, the
heating valve closes. If the freezestat closes again, the heating
valve opens, and the 10-minute timer resets.

When the freezestat opens again, the “Freeze Prob” alarm
automatically clears. This feature protects the coil and allows
the system to start normally after a cold night.

78 McQuay IM 893-1

Unit Options

External Time Clock or Tenant Override

There are several methods of switching the rooftop unit
between occupied and unoccupied operation. It can be done by
the controller internal schedule, a network schedule, an
external time clock, or a tenant override switch.

If the internal schedule or a network schedule is used, field
wiring is not required.

Figure 83: External Time Clock or Tenant Schematic

An external time clock or a tenant override switch can be used
by installing a set of dry contacts across terminals 101 and 102
on the field terminal block (TB2). When these contacts close,
24 V (ac) is applied to binary input MCB-DI3, overriding any
internal or network schedule and placing the unit into occupied
operation (provided the unit is not manually disabled). When
the contacts open (24 V (ac) is removed from MCB-DI3) the
unit acts according to the controller internal time schedule or a
network schedule. Refer to the unit wiring diagrams for
specific wiring termination details.

Field Output Signals

The following outputs may be available for field connections
to a suitable device.

VAV Box Signal/Fan Operation Signal

Digital Output #10 (MCB-DO10) may be selected as either the
Fan Operation output or the VAV output via the keypad. The
VAV/Fan Pop selection can be selected by accessing the Unit
Setup menu in the Extended Menu section.

Fan Operation

The Fan Operation Output (MCB-DO10) supplies 24 V (ac) to
terminal 116 on the field terminal block (TB2) when the output
is on. To use this signal, wire the coil of a field supplied and
installed 24 V (ac) pilot relay across terminals 116 and 117 on
TB2. When this output is on, 24 V (ac) is supplied from the T3
control transformer through the output relay to energize the
field relay. Refer to the as-built wiring diagrams.

The Fan Operation output is on when the unit is not Off and
when both the unit is Off and airflow is detected. It is off when
the unit is off and airflow is not detected.

VAV B ox O u tp u t

The VAV Box Output (MCB-DO10) supplies 24 V (ac) to
terminal 116 on the field terminal block (TB2) when the output
is on. To use this signal, wire the coil of a field supplied and
installed 24 V (ac) pilot relay across terminals 116 and 117 on
TB2. When this output is on, 24 V (ac) is supplied from the T3
control transformer through the output relay to energize the
field relay. Refer to the as-built wiring diagrams.

In the Heating state, the VAV Output is turned off to indicate
that hot air instead of the normal cool air is being supplied to
the VAV boxes. The VAV boxes are driven to their Heating
Position when hot air is provided based on either the normally
open or normally closed contacts of the VAV output. The VFD
will continue to be controlled to maintain the desired duct
static pressure. This output is also off when the unit is in the
Startup or Recirculation states. If this output is in the Heat (off)
position when the unit enters the Fan Only state or Minimum
DAT Control state, the output remains off for an adjustable
Post Heat Time (while the unit VFDs are driven to minimum
speed) or until the VFD gets to its minimum speed if the Post
Heat Time is set greater than 0. The Post Heat Timer can be
adjusted via the keypad/display Timer Setting menu in the
Extended Menus.

McQuay IM 893-1 79

Unit Options

During unoccupied operation, the VAV Box Output is in the
Cool (on) position unless airflow is detected. When airflow is
detected, it switches to the Heat (off) position.

Figure 84: Field Output Schematic

Entering Fan Temperature Sensor

The entering fan temperature (EFT) sensor and an associated
“Lo Airflow Problem” alarm are provided on VAV units with
MicroTech III control and gas or electric heat. The EFT sensor
is located in the supply fan section of the unit at the supply air
funnel.

Heat is disabled whenever the airflow is detected to be too low
for safe heating operation. This condition is indicated when the
supply air temperature exceeds the mixed air temperature by
more than 60°F (16°C).

Note: This value is not always 60°F. It depends on whether the

unit is gas or electric heat and on the burner/baffling
arrangement on gas heat units.

In this case, a “Lo Airflow Problem” alarm is generated and
heat is not enabled until the alarm is manually cleared. Refer to
the operation manual supplied with the unit for information
clearing alarms (OM 920).

Duct High Pressure Limit

The duct high pressure limit control (DHL) is provided on all
VAV units. The DHL protects the duct work, the terminal
boxes, and the unit from over pressurization, which could be
caused by, for example, tripped fire dampers or control failure.

The DHL control is factory set to open when the discharge
plenum pressure rises to 3.5" wc (872 Pa). This setting should
be correct for most applications; however, it is adjustable.
Removing the front cover of the device reveals a scale

showing the current setting. Turning the adjustment screw
(located on the bottom of the device) adjusts the setting up or
down.

If the DHL switch opens, digital input MCB BI 14 on the Main
Control Board de-energizes. The MicroTech III controller then
shuts down the unit and enters the Off-Alarm state. The alarm
must be manually cleared before the unit can start again. Refer
to the operation manual supplied with your unit for more
information on clearing alarms (OM 920).

Variable Frequency Drive Operation

Refer to the vendor instructions supplied with the unit.

Convenience Receptacle/Section Lights

A Ground Fault Circuit Interrupter (GFCI) convenience
receptacle is provided in the main control box on all units. One
of the following is required:

1 Connect a separate field-supplied 115 V power wiring

circuit to the 115V field terminal block TB7, located in the
main control box.

2 Select the factory powered outlet option at time of

purchase.

Optional lights are available for certain sections in the unit.
Each light includes a switch and convenience receptacle and is
powered by the external 115V power supply connected to
TB7.

80 McQuay IM 893-1

Unit Options

F11C

F11B

F11A

L1

L2

L3

L1

L2

L3

T1

T2

T3

V1A

OC

P24 F

Variable

Frequency

Drive

Pressure

Transducer

Mtr

R11

AFD11

Cndr Mtr #11

White

Black

Red

PB

Frequency

60 Hz

23 Hz

250 psig

(83°)

400 psig

(116°)

Condensing Pressure

Optional Low Ambient Compressor Operation

McQuay’s head pressure control operates in conjunction with
FanTrol by modulating the motor speed of the last condenser
fan of each refrigeration circuit in response to condenser
pressure. By varying the speed of the last condenser fan of
each refrigeration circuit, the VFD option allows mechanical
cooling operation in ambient temperatures down to 0°F (–
18°C). The VFD option senses refrigerant head pressure and
varies the fan speed accordingly. When the pressure rises, the
SpeedTrol increases the fan speed; when the pressure falls,
SpeedTrol decreases the fan speed.

The VFD throttling range is 250 to 400 psig, fixed. The VFD
fan motor is a three-phase motor, identical to the unit voltage
(208 V to 575 V) and is controlled by a variable frequency
drive (Figure 85). The variable frequency drive receives a

Figure 85: R-410A Speedtrol

signal from a pressure transducer and varies the condenser fan
speed accordingly.

The pressure transducer is calibrated to provide a 1.0 to 5.0 V
(dc) signal with a 8 to 30 V (dc) input, starting at 1.0 V (dc) @
250 psig and up to 5.0 V (dc) @ 400 psig. In order to maintain
an acceptable condensing pressure, the VFD will modulate the
motor down to a minimum of 23 Hz, and will not allow
operation below this frequency level. At, or above 400 psig,
the VFD will operate the motor at 60 Hz. The control band
between the two frequencies (23 Hz and 60 Hz) is a linear
relationship with the condensing pressure as shown in
(Figure 86).

The VFDs and pressure transducers are located in the control
box mounted in the condensing section. Each refrigerant
circuit is independent and has its own respective VFD and
pressure transducer. The speedtrol option operates
independently of the main unit controller.

Figure 86: Speedtrol Operating Characteristics

McQuay IM 893-1 81

Unit Options

Variable Frequency Drive Operation

Refer to the vendor instructions supplied with the unit.

Convenience Receptacle/Section Lights

A Ground Fault Circuit Interrupter (GFCI) convenience
receptacle is provided in the main control box on all units. To

use this receptacle, connect a separate field-supplied 115V
power wiring circuit to the 115V field terminal block TB7,
located in the main control box.

Optional lights are available for certain sections in the unit.
Each light includes a switch and convenience receptacle and is
powered by the external 115V power supply connected to
TB7.

DesignFlow™ Outdoor Air Damper Option

DesignFlow™ airflow measurement stations are located inside
the louvered outdoor air intake doors between the intake
louver and outside air dampers (Figure 87). Essentially, they
consist of a vane that is repositioned by airflow, the amount of
rotation indicating the amount of airflow. They are calibrated
precisely at the factory and no further calibration is required.
However, a leveling adjustment is required in the field so that
the DesignFlow unit is in the same orientation as when it was
factory calibrated. See “DesignFlow Station Startup” below.

The rotational position of the DesignFlow unit vane is
translated into CFM by the microprocessor in the MicroTech
III control system. The position of the vane is determined by
two things—the force of the airflow impacting the vane and
the gravitational effect on the vane. Gravity is the only factor
at the lower CFM end of the range. On a correctly leveled unit,
this gravitational effect will be the same as when the unit was
calibrated in the factory.

Accurately leveling a station involves applying a precise
mechanical force against the vane. This force should cause the
vane to move to a specific position if the DesignFlow unit is
correctly leveled.

DesignFlow Station Startup

Before initial startup of the rooftop unit, carry out the
following procedure on both the right-hand (control panel
side) and left-hand (side opposite the control panel)
DesignFlow station vanes (see Figure 87).

1 Verify that power is supplied to the unit’s MicroTech III

control system. The DesignFlow startup procedure cannot
be completed without use of the MicroTech III controls.

2 Unlock and open the louvered outdoor air intake door on

the side of the unit (see Figure 87).

3 The swinging vane on the measurement station is locked in

place for shipment. Unlock it by removing the two shipping
screws. One is located one inch from the top of the vane
and the other one inch from the bottom of the vane. Both
are about eight inches in from the outer edge of the vane.

4 Examine the station for shipping damage. Manually rotate

the vane and verify that it does not rub against anything.

Figure 87: DesignFlow Station

Manually hold the vane closed against the mechanical stop

5

at the top of the assembly. Then, read the current vane
leveling position on the MicroTech III keypad/display.

Do this by viewing the LH Lvl Pos= or RH Lvl Pos=
parameter in the DesignFlow setup menu. The LH Lvl
Pos= parameter indicates the current position of the vane
for the left-hand DesignFlow station (side opposite the
control panel). The RH Lvl Pos= parameter indicates the
current position of the vane for the right-hand DesignFlow
station (control panel side).

Important: Wait several seconds until the value on the
keypad stabilizes before taking the reading.

For detailed information regarding operation and
navigation through the unit keypad, refer to OM 137
(discharge air control units) or OM 138 (zone control
units).

6 Confirm the value of the reading. Ideally, it should read

close to 20.00 (19.50 to 20.50 is acceptable). If the reading
is out of range, loosen the screws fixing the mechanical
stop at the top of the assembly, make a small adjustment,
and recheck until the reading is in the specified range.

Note: Generally, adjustments should not be necessary.

7 Locate the leveling component kit, which is shipped with

the unit, in the unit main control panel.

82 McQuay IM 893-1

Unit Options

Vane

Duct tape

This edge flush
with this side of vane

These edges flush
with bottom of vane

Fulcrum alignment plate

Fulcrum

Duct tape

8 Duct tape the fulcrum alignment plate to the bottom corner

of the vane (see Figure 88) aligning it as follows:

a The bottom edge of its notches should be flush with the

bottom edge of the vane.

b The side of one notch should be even with the bend near

Note: The alignment mark is located 0.50 inch in from

the bend on the outer edge of the vane. It
intersects with a hole located one inch up from
the bottom outer edge of the vane.

Figure 89: Place Leveling Weight on Fulcrum

the outer edge of the vane.

c The plate should be flat against the outer surface of the

vane.

Figure 88: Tape Fulcrum Alignment Plate to Vane

9 Locate and install the fulcrum used in the leveling

procedure as follows (see Figure 88):

a Wipe the bottom of the louver door where the fulcrum

will be located so that the duct tape will stick to it.

b Pre-apply duct tape to the top surface of the bottom

portion of the fulcrum, extending it about one inch
beyond the edges on three sides.

Set up the leveling test as follows:

c With the alignment plate taped to the vane and the vane

in the zero airflow position, locate the fulcrum parallel
to and against the alignment plate.

Note: The zero airflow position is when the vane is

swung away from the back wall and gently resting
against its stop.

d Once the fulcrum is in position, press the duct tape

extensions down to hold the fulcrum in place.

e Remove the alignment plate after installing the fulcrum.

10 Close and latch the louvered intake door.

11 Remove the cover from the access opening in the bottom

blade of the outdoor air intake louver (see Figure 91).

12 Verify that the unit fans are off and that the outdoor air

dampers are closed. If there is a wind, cover the outdoor air
louvers with poly film, cardboard, or other suitable material
to prevent adverse readings due to wind.

13 Rest the leveling weight assembly on the fulcrum, as shown

McQuay IM 893-1 83

in Figure 89, so that:

a Its bottom two thumbscrews rest on the top edge of the

fulcrum.

b Its top thumbscrew rests against the vertical alignment

mark on the vane.

14

a While holding the weight so it stays on the fulcrum,

manually rotate the vane to the wide-open position,
manually return it to the zero CFM position, and gently
release the vane.

b Locate the leveling weight assembly so its contact point

is against the vertical mark on the vane.

c While the weight assembly teeters on the fulcrum,

gently rap the base frame to slightly vibrate the
assembly and encourage the vane to seek its equilibrium
point.

15 Read the current LH Lvl Pos= (or RH Lvl Pos=) parameter

in the DesignFlow Setup menu on the keypad/display.
These parameters vary from 20% to 80% depending on the
position of the DesignFlow vane

16 If the value indicated by the LH Lvl Pos= (or RH Lvl Pos=)

parameter is not within the range of 22.56% to 23.02%
(22.79% is ideal), adjust the level of the DesignFlow unit

using the procedure described in “Making Level
Adjustments” below.

17 When the LH Lvl Pos= (or RH Lvl Pos=) value is in range,

remove the fulcrum and leveling weight assembly and
replace the access opening cover in the louvered door.

Unit Options

Top lock nuts

Vane

Bottom lock nut

Pivot point

Access opening

Louvered
door

Threaded adjuster

assembly

Long adjuster nut

Jam nuts

Locknut

To INCREASE L dimensionLTo INCREASE L dimension

L

Right hand adjuster Left hand adjuster

Making Level Adjustments

The DesignFlow unit is mounted so that it pivots at the top
when three lock nuts are loosened, two at the top and one at
the bottom of the assembly (see Figure 90). Leveling the unit
involves precisely pivoting the assembly with a known force
applied to the vane until the vane opens to a specific position.

If after performing Steps 13 through 15 above, the vane does
not come to rest within the specified range, carry out the
following steps:

1 Unlock and open the louvered outdoor air intake door on

the side of the unit.

2 Loosen the two .25-20 NC lock nuts at the top of the

DesignFlow frame. (See Figure 90.)

Figure 90: DesignFlow Frame

7 When finished making the adjustments, tighten the .25-20

NC lock nut in the slotted hole at the bottom of the
DesignFlow frame. (See Figure 92.)

Note: Make sure the leveling weight’s top thumbscrew is still

against the vertical alignment mark on the vane.

8 Gently rap the base frame to slightly vibrate the assembly

to encourage the vane to seek its equilibrium point.

9 Recheck the vane position compared to the range specified

in Step 16 above. Readjust the level as necessary.

Note: If large adjustments are required to correctly level the

vane assembly, before rechecking the level, relocate the
fulcrum as described in Step 9 in “DesignFlow Station
Startup” on page 82.

10 When the level is correct, unlock and open the louvered

outdoor air intake door on the side of the unit and tighten
the two .25-20 NC lock nuts at the top of the DesignFlow
frame. (See Figure 90.)

11 Close and lock the air intake door.

12 Recheck the vane position and readjust the level as

necessary.

13 When the vane position is correct, remove the fulcrum and

replace the access opening cover in the louvered door.

3

Close and lock the intake door.

4 Remove the cover from the access opening in the bottom

blade of the outdoor air intake louver (see Figure 91).

5 Loosen the .25-20 NC lock nut in the slotted hole at the

bottom of the DesignFlow frame. (See Figure 92.)

6 If the LH Lvl Pos= (or RH Lvl Pos=) value obtained in

step 15 above is HIGHER than the specified range,
move the bottom of the DesignFlow frame closer to the
outdoor air dampers (away from the back end of the unit).
Do this by turning the long adjuster nut to increase the L
dimension in Figure 92.

If the LH Lvl Pos= (or RH Lvl Pos=) value obtained in
step 15 above is LOWER than the specified range,

move the bottom of the DesignFlow frame away from the
outdoor air dampers (toward the back end of the unit). Do
this by turning the long adjuster nut to decrease the L
dimension in Figure 92.

Note: If the necessary adjustment cannot be made using

the long adjuster nut, reposition the two .25-20 NC
jam nuts on the threaded rod to make larger
adjustments (see Figure 92).

Figure 91: Remove Covers from Access Opening

Figure 92: Leveling Adjustment

84 McQuay IM 893-1

Propeller Exhaust Fan Option

Fans and motors

VFD

Starters

A i r f l o w

A i r f l o w

R o t a t i o n

R o t a t i o n

Unit Options

Economizer units may include propeller exhaust or centrifugal
return fan options. This section covers maintenance and
operating instructions for the propeller exhaust option.
Centrifugal return fan construction, maintenance and operation
is similar to that for supply fans and covered in other sections
of this manual.

Figure 93: Two Fans with Back Return Shown

number of turns open. Any increase in fan speed represents a
substantial increase in horsepower required from the motor.
Always check motor load amperage and compare to name
plate rating when changing fan speed.

Figure 94: Fan Rotation

Once the fan is put into operation, set up a periodic
maintenance program to preserve the reliability and
performance of the fan. Items to include in this program are:

• Belts

• Bearings

• Fasteners

• Setscrews

• Lubrication

• Removal of Dust/Dirt

Prestarting Checks

Check all fasteners and set screws for tightness. This is
especially important for bearing set screws.

The propeller should rotate freely and not rub on the fan panel
venturi. Rotation direction of the propeller should be checked
by momentarily turning the unit on. Rotation should be in the
same direction as the rotation decal affixed to the unit or as
shown in Figure 94. For three-phase installations, fan rotation
can be reversed by simply interchanging any two of the three
electrical leads.

The adjustable motor pulley is preset at the factory for the
specified fan RPM. Fan speed can be increased by closing or
decreased by opening the adjustable pulley. Two or three
groove variable pitch pulleys must be adjusted an equal

Damper Counterbalance Adjustment

The following instructions should be followed when
attempting to maximize the counterbalance effect on the EM
or GM model dampers. Be aware that when the balance setting
is highly sensitive, friction wear and contamination will have
an adverse effect to the operation of the damper. The
sensitivity of the counterbalance should only be set to meet the
application requirements. The damper must be mounted square
and plumb and operate freely before any weight adjustments
are performed.

Adjustment #1 will effect the balance of the blades in the open
position. Adjustment #2 will effect the balance of the blades in
the closed position along with a small change to the open
position balance.

If the damper blades do not achieve full open position under
airflow and you want them to open further or all the way, then
adjustment #1 will need to be performed. If the damper blades
do not open completely and adjustment #1 has been addressed,
then more weight is required.

If the airflow through the damper is light and the blades only
slightly move from the closed position, then adjustment #2 and
#1 are required.

McQuay IM 893-1 85

Unit Options

Bend Here

Mounting
Bracket Slot

B e l t S p a n

D e f l e c t i o n =

B e l t S p a n

6 4

Adjustment #1:

Moving the weight stack along the length of the mounting
bracket slot (Figure 95) will effect the full open balance of the
blade assembly. Moving the weights further away from the
blade pivot point will cause the blades to become more
balanced so that at some point, and with enough weight, the
blades would remain open. Care must be taken to ensure that
when the weights are moved outward from the blade pivot
point they will not interfere with the adjacent blade when the
blades close. Moving the weights back towards the blade pivot
point will allow the blades to close.

Figure 95: Counterbalance Adjustment

Note: Performing adjustment #2 will have a small effect on

adjustment #1. Therefore, if adjustment #1 is critical,
then adjustment #1 may need to be repeated.

Belts

Premature belt failures are frequently caused by improper belt
tension (either too tight or too loose) or misaligned pulleys.
The proper tension for operating a V-belt is the lowest tension
at which the belts will not slip at peak load conditions. For
initial tensioning, the proper belt deflection half way between
pulley centers is 1/64" for each inch of belt span. For example,
if the belt span is 64 inches, the belt deflection should be one
inch using moderate thumb pressure at midpoint of the drive,
See Figure 96.

Check belt tension two times during the first 24 hours of
operation and periodically thereafter. To adjust belt tension,
simply loosen four fasteners (two on each side of the motor
plate) and slide the motor plate away from the fan shaft until
proper belt tension is attained. On some fans, fasteners
attaching the motor to the motor plate must be loosened in
order to adjust the belt.

It is very important that the drive pulleys remain in proper
alignment after adjustments are made. Misalignment of pulleys
results in premature belt wear, noise, vibration, and power loss.

See Figure 97.

Adjustment #2:

The damper is assembled with the counterbalance weights and
bracket installed such that, when the blades are closed, the
counterbalance weights and bracket are positioned directly
inline with the blade pivot points. This position of the weights
will provide a slight load that will hold the blades in the closed
position. To reduce this load, the counterweight-mounting
brackets can be bent (Figure 95) away from the adjacent blade
surface. Bending the counterweight mounting brackets will
move the counterweight stack behind the blade pivot point and
therefore allow the blades to start opening at lower airflow
rates. This adjustment should be performed in small
increments since the blades will not fully close if the brackets
are bent to far.

WARNING

Rotating parts can cause severe personal injury or death.
Replace all belt/fan guards that are removed temporarily for
service.

Figure 96: Belt Adjustment

86 McQuay IM 893-1

Figure 97: Drive Pulley Alignment

C e n t e r l i n e s
m u s t c o i n c i d e

M u s t b e
p a r a l l e l

M u s t b e
p a r a l l e l

A d j u s t a b l e
S h e a v e

M o t o r

B e a r i n g

9

8

7

1 0

6

5

4

1

2

3

1 . F a n pa n e l
2 . P r o p e l l e r
3 . D r i v e fr a m e
ch a n n e l ( 2 )
4 . M o to r pl a te
5 . M o to r
6 . M o to r pu l l e y
7 . S h a ft pu l l e y
8 . F a n sh a ft

9 . B e a r i n g s
1 0. B e l t
1 1. B e

a r i n g pl a te

11

Unit Options

Table 17: Propeller Exhaust Fan Troubleshooting

Problem Cause Corrective Action

Reduced

Airflow

System resistance is too
high.

Unit running backwards. See “Prestarting Checks” on page 85
Fan speed too low. Increase fan speed

Check backdraft dampers for proper operation. Remove obstructions in ductwork. Clean dirty filters.
Check for adequate supply for air exhaust fans or exhaust air for supply fans.

Excessive dirt on propeller. Clean propeller
Bearings Tighten bearing collars and setscrews. Lubricate bearings. Replace defective bearings.

Excessive

Noise

V-Belt drive Tighten pulleys on motor shaft and fan shaft. Adjust belt tension. Align pulleys. Replace worn belts or pulleys.
Excessive vibration Clean dirt build-up from propeller. Check all setscrews and fasteners for tightness. Check for worn bearing.

Correct propeller imbalance. Check for loose dampers, guards or ductwork.

Defective motor Replace motor.

Figure 98: Propeller Exhaust Fan Replacement Parts List

McQuay IM 893-1 87

Unit Options

Ultraviolet

Light
Units

Light Power
Disconnect
Switch

Light Power
Disconnect
Switch

View
Window

Cooling
Coil

AIRFLOW

Bearings

Bearings are the most critical moving part of the fan; inspect
them at periodic intervals. Check locking collars, set screws,
and fasteners that attach bearings to the bearing plate for
tightness. In a clean environment and temperatures above
32°F/below 200°F, lubricate fan shaft bearings with grease
fittings semiannually using a high quality lithium-based
grease. If unusual environmental conditions exist temperatures
below 32°F/above 200°F, moisture or contaminants, more
frequent lubrication is required.

With the unit running, add grease very slowly with a manual
grease gun until a slight bead of grease forms at the seal. Be
careful not to unseat the seal by over lubricating or using
excessive pressure. Bearings without grease fittings are
lubricated for life.

Fasteners and Setscrews

Any fan vibration has a tendency to loosen mechanical
fasteners. A periodic inspection should include checking all
fasteners and set screws for tightness. Pay particular attention
to setscrews attaching the propeller to the shaft and the shaft to
the bearings. Loose bearing set screws lead to premature
failure of the fan shaft.

Lubrication

Refer to “Bearings” for bearing lubrication. Many fractional
horsepower motors installed on the smaller fans are lubricated
for life and require no further attention. Oil motors equipped
with oil holes in accordance with the manufacturer’s
instructions printed on the motor. Use a high grade SAE 20
machine oil and use caution not to over lubricate. Grease
motors supplied with grease fittings according to directions
printed on the motor.

Exhaust Fan Troubleshooting

Table 17 provides guidelines for troubleshooting problems
with the propeller exhaust fan options. A list of parts is
provided in Figure 99.

Ultraviolet Lights Option

When this option is employed, ultraviolet C light bathes the
moist surfaces on the coil and drain pan, killing most
microorganisms that can grow there.

Typically, ultraviolet lights are installed on the leaving side of
the cooling coils in the unit. Each light module is mounted on a
rail and is removable for convenient bulb replacement.

UV Light Power Disconnect switches (two per door) are
factory installed on every door that allows a direct line of sight
to the UV lamps when opened. These switches are designed to
prevent UV exposure when cabinet doors are opened and must
not be disabled.

A viewing window near the UV lights allows viewing to
determine if the lights are energized. The viewing windows
use specially designed glass that blocks harmful UV light.

WARNING

UVC exposure is harmful to the skin and eyes. Looking at an
illuminated bulb can cause permanent blindness. Skin
exposure to UVC can cause cancer.
Always disconnect power to unit before servicing. Do not
operate if disconnect switch has been disabled.

Figure 99: Typical Ultraviolet Light Installation

Removing Dust/Dirt

Thoroughly clean the exterior surface of the motor, fan panel,
and entire propeller periodically. Dirt can clog cooling
openings on motor housings, contaminate bearing lubricant,
and collect on propeller blades causing severe imbalance if left
unchecked. Use caution and do not allow water or solvents to
enter the motor or bearings. Under no circumstances should
motors or bearings be sprayed with steam or water.

Exhaust Fan On/Off Control

The exhaust fans are turned on and off based on building static
pressure, outdoor air damper position, and discharge fan
capacity. Exhaust fans do not have to always run while the
supply fan is on, as does a return fan. They are turned on and
off through output MCB-B02 on the Main Control Board. For
detailed information on Propeller Exhaust Fan Control, see the
operation manual supplied with the unit (OM 920).

88 McQuay IM 893-1

Unit Options

Ultraviolet Light Operation

Refer to the wiring schematic below. 115 V (ac) power for the
UV lights is provided by control circuit transformer T1. The
lights operate whenever the unit is powered, system switch S1
is closed, and all doors with door power disconnect switches
are closed. To turn the lights off, disconnect power to the entire
unit, or open system switch S1.

Figure 100: Typical Ultraviolet Light Wiring Schematic

The normally open disconnect switches are wired in series in a
circuit that supplies 24 V (ac) to the coil of relay R45. When
all doors are closed, relay R45 is energized, and its normally
open contacts (in series with system switch S1) provide 115 V
(ac) to the UV lights.

McQuay IM 893-1 89

Unit Options

MicroTech® III Remote User Interface for McQuay
Rooftop and Self-Contained Systems

In addition to the unit-mounted user interface provided with
MicroTech III controls, McQuay applied rooftop systems and
indoor vertical self-contained systems can be equipped with a
remote user interface that handles up to eight units per
interface. The remote user interface provides convenient
access to unit diagnostics and control adjustments, without
having to access your roof or mechanical rooms located on
each floor.

Each remote user interface offers the same functionality as its
unit-mounted counterpart, including:

• Push-and-roll navigation wheel with an 8-line by 30­character display format.

• Digital display of messages in English language.

• All operating conditions, system alarms, control parameters

and schedules are monitored.

Figure 102: Process Bus Wiring Connections

Re mote HMI

CE + CE-

Unit #1 MC B Unit #2 MC B Unit #3 MC B

CE + CE-

CE + C E+CE - C E-

Features

• Can be wired up to 700 meters from units for
flexibility in placing each remote user interface within
your building.

• Unit and remote user interfaces are both active.

Figure 101: Remote User Interface

BL K WH T

BL K WH T

BL K WH T BL K WHT

Daisy-chain up to 8 units to a
single remote interface

90 McQuay IM 893-1

Figure 103: Specifications and Connections

Unit Options

McQuay IM 893-1 91

Check, Test, and Start Procedures

Check, Test, and Start Procedures

All units are completely run tested at the factory to promote
proper operation in the field. Nevertheless, the following
check, test, and start procedures must be performed to properly
start the unit. To obtain full warranty coverage, complete and
sign the check, test, and start form supplied with the unit, or
complete the “Rooftop Equipment Warranty Regist. Form” on
page 121 and return it to McQuay International.

WARNING

Electric shock and moving machinery hazard. Can cause
severe equipment damage, personal injury, or death.

Disconnect and tag out all electrical power before servicing this
equipment.

All start-up and service work must be performed only by trained,
experienced technicians familiar with the hazards of working on
this type of equipment.

Read and follow this manual: “MicroTech III Applied Rooftop
Unit Controller” manual (OM 920) before operating or servicing.

Bond the equipment frame to the building electrical ground
through grounding terminal or other approved means.

A representative of the owner or the operator of the equipment
should be present during start-up to receive instructions in the
operation, care, and maintenance of the unit.

If the unit has a factory mounted disconnect switch, use the
switch’s bypass mechanism to open the main control panel
door without de-energizing the control panel. See page 117 for
instructions.

Servicing Control Panel Components

WARNING

Hazardous voltage. May cause severe injury or death.
Disconnect electric power before servicing equipment. More
than one disconnect may be required to de-energize the unit.

Disconnect all electric power to the unit when servicing
control panel components. Unless power is disconnected to the
unit, the components are energized. Always inspect units for
multiple disconnects to ensure all power is removed from the
control panel and its components before servicing.

Before Start-up

1 Verify that the unit is completely and properly installed

with ductwork connected.

2 Verify that all construction debris is removed, and that the

filters are clean.

3 Verify that all electrical work is complete and properly

terminated.

4 Verify that all electrical connections in the unit control

panel and compressor terminal box are tight, and that the
proper voltage is connected.

5 Verify all nameplate electrical data is compatible with the

power supply.

6 Verify the phase voltage imbalance is no greater than 10%.

7 Verify that gas piping is complete and leak tight.

8 Verify that the shutoff cock is installed ahead of the

furnace, and that all air has been bled from the gas lines.

9 Manually rotate all fans and verify that they rotate freely.

10 Verify that the belts are tight and the sheaves are aligned.

11 Verify that all setscrews and fasteners on the fan assemblies

are still tight. Do this by reading and following the
instructions in “Setscrews,” which is in the “Maintenance”
section of this manual.

12 Verify that the evaporator condensate drain is trapped and

that the drain pan is level.

13 If unit is curb mounted, verify that the curb is properly

flashed to prevent water leakage.

14 Before attempting to operate the unit, review the control

layout description to become familiar with the control
locations.

15 Review the equipment and service literature, the sequences

of operation, and the wiring diagrams to become familiar
with the functions and purposes of the controls and devices.

16 Determine which optional controls are included with the

unit.

17 Before closing (connecting) the power disconnect switch,

open (disconnect) the following unit control circuit
switches:

a Main Control Panel

– Turn system switch S1 to OFF.

– Electric heat units: turn switch HS1 to OFF.

b Furnace Control Compartment

– Turn furnace switch S3 to OFF.

– Main Control Panel Switch

18 If the DAC or SCC unit does not have an optional zone

S7 to OFF.

temperature sensor (ZNT1) connected to it, you may need
to change the keypad entry under Setup/Service \ Unit
Configuration \ Space Sensor= from YES to NO.

Note: If desired, you can significantly reduce all MicroTech

III internal control timers by the changing the entry
under keypad menu Setup/Service\Unit

Configuration\Timer Settings\Service= from 0 min to X
min where X is the number of minutes you want the unit

to operate with fast timers.

Power Up

1 Close the unit disconnect switch. With the control system

switch S1 in the OFF position, power should be available
only to the control circuit transformer (T1) and the
compressor crankcase heaters.

2 Turn the Switch S1 to ON. Power should now be supplied

to the control panel, and the LEDs on MCB1 should follow
the normal startup sequence (refer to “Power-up” on page

50).

92 McQuay IM 893-1

Check, Test, and Start Procedures

1.21"

Fan Start-up

1 Verify all duct isolation dampers are open. Unit mounted

isolation dampers may be in the supply or return sections.

2 Place the unit into the Fan Only mode through the keypad

menu System Summary\System\Ctrl Mode= Fan Only.

3 Turn Switch S7 to ON. The controller should enter the

Startup Initial operating state. If the fan does not run:

a Check fuses F1 and F3.

b Check the manual motor protectors or that the circuit

breakers have not tripped.

c Check the optional phase monitor.

4 If the fans are equipped with optional spring isolators,

check the fan spring mount adjustment. When the fans are
running they should be level. Refer to “Spring Isolated
Fans” on page 47.

5 Verify the fan rotation is correct.

6 Verify the DHL safety is opening at a pressure compatible

with duct working pressure limits.

Note: The supply and return fan drives usually are selected for

operation in the drive's midspeed range. The return fan
drives are usually shipped with fixed pitch sheaves that
will provide the selected fan speed; however, the supply
fan drives are usually shipped with variable pitch
sheaves that are adjusted to provide the minimum fan
speed. Both drives should be adjusted for proper airflow
during air balancing. See“Air Balancing” on page 96.

Economizer Start-up

CAUTION

Adjust dampers properly. Improper adjustment can
damage the dampers. When an economizer is ordered

without an actuator, the linkage requires a 3.14" linear stroke to
open it fully. Do not allow dampers to be driven beyond their
normal full closed or full open position.

1 Check whether the outdoor air is suitable for free cooling

by displaying the keypad menu Temperature\OA
Damper\OA Ambient=. Low indicates low outdoor air

enthalpy; High indicates high outdoor air enthalpy. See
“Enthalpy Control” on page 73 to verify that the enthalpy
changeover control is working properly. You may want to
take temperature and humidity measurements.

2 At the keypad, set the cooling setpoint low enough so the

controller calls for cooling. Adjust the value in
Temperature\Zone Cooling\Occ Clg Spt= below the
temperature shown in Temperature\Zone Cooling\Control

Te mp =. In addition, on DAC units, adjust the value in
Temperature\Discharge Cooling\DAT Clg Spt= below the
temperature shown in Temperature\Discharge
Cooling\Disch Air=.

3 Place the unit into cooling mode through the keypad menu

System Summary\System\Ctrl Mode= Cool Only.

4 Observe the outdoor air dampers:

a If the outdoor enthalpy is low, the control algorithm

should start to modulate the dampers open to maintain
the discharge air setpoint.

b If the outdoor enthalpy is high, the dampers should

maintain their minimum position. Look at menu
Temperature\OA Damper\MinOA Pos=. Change this
entry to another value. Verify that the dampers move to
the new minimum position setpoint.

5 If the unit is equipped with the electromechanical enthalpy

changeover control (Honeywell H205) and the outdoor air
condition is borderline, attempt to change its input to the
MicroTech III controller by turning the switch adjustment
to A or D. Check enthalpy status in keypad menu
Temperature \ OA Damper \ OA Ambient=. If this reading
is Low, go to Step 5a. If it is High, go to Step 5b.

Note: It may not be possible to check the economizer

operation in both low and high enthalpy states on the
same day. If this is the case, repeat this procedure on
another day when the opposite outdoor air enthalpy
conditions exist.

Compressor Startup

With the supply and return fans operational, prepare for
compressor operation.

CAUTION

Low ambient temperature hazard. Can cause compressor
damage. Do not attempt to start up and check out the

refrigeration system when the outdoor air temperature is below
50°F unless the unit is specially equipped for low ambient
operation.

The unit is shipped with the refrigeration service valves
closed. Open the discharge and liquid line valves.The
discharge valve is a quarter-turn ball valve. The liquid line is a
king valve and is opened by backseating the valve and then
cracking the valve off the backseat position (one turn forward).
Verify that the unit has not lost its refrigerant charge.

Verify that the crankcase heaters are operating. These should
operate for at least 24 hours before starting the compressors.

Verify that the condenser fan blades are positioned properly
and that the screws are tight (see Figure 104). The fan blade
must be correctly positioned within its orifice for proper
airflow across the condenser coils.

Figure 104: Condenser Fan Blade Positioning

McQuay IM 893-1 93

Check, Test, and Start Procedures

Scroll Compressor Rotational Direction

Scroll compressors only compress in one rotational direction.
Three-phase compressors can rotate in either direction
depending upon phasing of the power to L1, L2, and L3. Since
there is a 50/50 chance of connecting power to cause rotation
in the reverse direction, verify that the compressor rotates in
the proper direction after the system is installed. If the
compressor is rotating properly, suction pressure drops and
discharge pressure rises when the compressor is energized. If
the compressor is rotating in reverse, the sound level is louder
and current draw is reduced substantially. After several
minutes of operation, the compressor’s motor protector trips.

All three-phase compressors are wired the same internally.
Therefore, once the correct phasing is determined for a specific
system or installation, connecting properly phased power leads
to the same terminals should maintain proper rotational
direction.

Perform the following procedure on all units:

1 At the keypad, set the cooling setpoint low enough so that

the controller will call for cooling. The value in
Temperature \ Zone Cooling \ Occ Clg Spt= will need to be
adjusted below the temperature shown in Temp e ra t ure \
Zone Cooling \ Control Temp=. In addition, on DAC units,
the value in Temperature \ Discharge Cooling \ DAT Clg
Spt= will need to be adjusted below the temperature shown
in Temperature \ Discharge Cooling \ Disch Air=.

2 Place the unit into cooling mode through the keypad menu

System Summary \ System \ Ctrl Mode= Cool Only.

3 Verify that the low ambient compressor lockout

temperature setpoint, Temperature \ OA Damper \
OATComp Lock= is set below the current outside air
temperature (shown in System Summary \ Temperatures \
OA Temp=).

Note: Do not attempt to operate the compressors if the outdoor

air is too cool. See the caution statement under
“Compressor Startup”.

4 Close the S1 switch. Now refrigeration circuit #1 is enabled

and circuit #2 is disabled. After CS1 is closed, the MT III
board starts its 5-minute timing cycle. Note that if the unit
has an economizer and the outdoor air enthalpy is low, the
economizer must fully open before the controller will
energize mechanical cooling.

5 When the outdoor air damper has fully opened and the time

delay has expired, the liquid line solenoid SV1 and the
compressor should start.

a Verify that there is a call for cooling by checking the

keypad menu System Summary \ System \ UnitStatus=.
This should be in Cooling.

b Check the keypad menu System Summary \ System \ Clg

Status=. The compressors will only run if this reads
either All Clg or Mech Clg.

c Trace the control circuits.

NOTICE

Venting refrigerant to atmosphere is not allowed per most
local laws and/or codes.

6 Verify that compressor #1 starts. If the compressor motor

hums but does not run, verify that it is getting three-phase
power.

7 The compressor should operate continuously while there is

a call for cooling. If the compressor cycles on its low
pressure switch, do the following:

a Verify that the circuit is not short of refrigerant.

b Check for low airflow.

c Check for clogged filters.

d Check for restricted ductwork.

e Check for very low temperature return air entering the

unit.

f Verify that the liquid line components, expansion valve,

and distributor tubes are feeding the evaporator coil.

g Verify that all air handling section panels are closed.

h Verify that the liquid line service valves are completely

open.

8 Verify that the compressors stage properly. As the circuit

loads up the second compressor (if available) will be
energized. For more information on staging sequences,
refer to IM 919 and OM 920.

9 Verify that the condenser fans are cycling and rotating

properly (blowing air upward). When the compressor
starts, at least one condenser fan should also start. The
CCB1 should control the remaining condenser fans based
on ambient air conditions. Look at keypad menu Setup/

Service \ Compressor Setup \ Cond Fan1= (also look at
Cond Fan2=, Cond Fan3=, Cond Fan4=). Table 3 on

page 17 and Table 4 on page 18 shows recommended
setpoints based on the unit size. Cond Fan1 controls BO5,
Cond Fan2 controls BO6, Cond Fan3 controls BO7, Cond
Fan4 controls BO8. Refer to the unit wiring diagrams and
“Condenser Fan Arrangement” on page 19.

10 Check the oil level in the compressor sightglass. If low oil

or heavy foaming is observed, it is possible that liquid
refrigerant is returning to the compressor. Check the
suction superheat (see “Expansion Valve Superheat
Adjustment” on page 95). It should be between 10°F
(5.5°C) and 13°F (7.2°C).

11 Open S1. the compressor should stop. Place the unit into

the “Fan Only” mode through the keypad menu System
Summary \ System \ Ctrl Mode= Fan Only.

12 Check refrigerant circuit #2 by repeating steps 2 through 9,

substituting circuit #2 nomenclature for circuit #1
nomenclature (CS2, TD2, CCB2, and compressor #2 (and
#4).

94 McQuay IM 893-1

Check, Test, and Start Procedures

13 Verify that the condenser refrigerant subcooling at full

capacity is between 13 and 20°F.

Expansion Valve Superheat Adjustment

It is very important that the expansion valve superheat setting
be adjusted to be between 10°F (–12°C) and 13°F (–11°C).
Insufficient superheat will cause liquid floodback to the
compressor which may result in slugging. Excessive superheat
will reduce system capacity and shorten compressor life.

Turn the adjustment stem clockwise to increase superheat. Not
exceeding one turn, adjust the stem and then observe the
superheat. Allow up to 30 minutes for the system to rebalance
at the final superheat setting.

On refrigeration circuits with multiple expansion valves, the
superheat adjustment should be approximately the same for all
valves in the circuit.

Checking Superheat

Following are recommendations for checking superheat:

1 Close the unit section doors. Running the unit with its

doors open will affect expansion valve and system
operation considerably.

2 For units with one expansion valve per circuit, check the

pressure and temperature at the compressor suction valve.

3 For units with multiple expansion valves per circuit, check

the pressure at the compressor, and check the temperature
at the suction header that is fed by the valve.

Note: If low oil level is accompanied by heavy foaming

visible in the oil sightglass, it is possible that excess
liquid refrigerant is returning to the compressor
depending on the rotation of the crank shaft. Check the
suction superheat and adjust the expansion valve for
10°F (–12°C) to 13°F (–11°C) of superheat. If proper
superheat is obtained, sightglass foaming is not a
concern.

Heating System Startup

General

1 At the keypad, set the heating setpoints high enough so that

the controller calls for heating.Adjust the value in
Temperature \ Zone Heating \ Occ Htg Spt= above the
temperature shown in Temperature \ Zone Heating \
Control Temp=. In addition, on DAC units, adjust the value
in Temperature \ Discharge Heating \ DAT Htg Spt= above
the temperature shown in Temperature \ Discharge Heating
\ Disch Air=.

2 Place the unit into heating mode through the keypad menu

System Summary \ System \ Ctrl Mode= Heat Only.

3 Verify that the high ambient heat lockout temperature

setpoint, Temperature \ Zone Heating \ OATHtg Lock= is
set above the current outside air temperature (shown in
System Summary \ Temperatures \ OA Temp=).

Gas Furnace

Refer to the “Start-up and Operating Procedures” section of
the Forced Draft Gas Fired Furnace Installation Manual, IM
684 or IM 685. Perform the start-up procedures given in it.

Electric Heat

Turn the electric heat switch HS1 to ON. The electric heaters
should energize. If the unit has multistage electric heat, the
MicroTech III Auxiliary Control board EHB1 should energize
the heaters in successive stages. The rate of staging is set in
keypad menu Setup/Service \ Heating Setup \ Stage Time=. The
default value of 5 min”can be adjusted from 2 to 60 minutes.

Steam Heat

The steam valve actuator should open the valve. The steam
valve is open when the valve stem is up. If the unit loses
power, the spring in the actuator should drive the valve wide
open. Check this by opening system switch S1.

For RCS/RFS applications in which the condensing section is
remote from the air handling section, consideration should
have been given to proper piping between the sections, as this
can affect the compressor oil level. Refer to the “ASHRAE
Handbooks” for more information on proper refrigeration
piping design and installation.

McQuay IM 893-1 95

Hot Water Heat

The hot water valve actuator should open the valve to the coil.
The three-way hot water valve is open to the coil when the
valve stem is down. If the unit loses power, the spring in the
actuator should drive the valve wide open to the coil. Check
this by opening system switch S1.

Check, Test, and Start Procedures

C e n t e r l i n e s
m u s t c o i n c i d e

M u s t b e
p a r a l l e l

M u s t b e
p a r a l l e l

A d j u s t a b l e
S h e a v e

M o t o r

B e a r i n g

Air Balancing

Air balancing should be performed by a qualified air balancing
technician. Note that the supply fan motors are usually shipped
with variable pitch sheaves which are typically set at the low
end of the drive’s fan rpm range. See “Mounting and Adjusting
Motor Sheaves” on page 97. The return fan motors are usually

shipped with fixed pitch sheaves.

WARNING

Moving machinery hazard. Can cause severe personal
injury or death.

Do not use a mechanically driven tachometer to measure the
speed of return fans on this fan arrangement. Use a strobe
tachometer.

The following should be performed as part of the air balancing
procedure:

1 Check the operating balance with the economizer dampers

positioned for both full outdoor air and minimum outdoor air.

2 Verify that the total airflow will never be less than that

required for operation of the electric heaters or gas furnace.

3 For VAV units that have fan tracking control, adjust the

supply/return fan balance by using the MicroTech III
controller's built-in, automatic capability. For complete
information on using this feature, see OM 920, MicroTech
III Applied Rooftop Unit Controller.

4 When the final drive adjustments or changes are complete,

check the current draw of the supply and return fan motors.
The amperage must not exceed the service factor stamped
on the motor nameplate.

5 Upon completion of the air balance, replace variable pitch

motor sheaves (if any) with comparably sized fixed pitch
sheaves. A fixed pitch sheave will reduce vibration and

provide longer belt and bearing life.

WARNING

Rotating parts can cause severe personal injury or death.

Replace all belt/fan guards that are temporarily removed for
service.

Sheave Alignment

Mounting:

1 Verify both driving and driven sheaves are in alignment and

the shafts are parallel. The center line of the driving sheave
must be in line with the center line of the driven sheave.
See Figure 105.

2 Verify that all setscrews are torqued to the values shown in

Table 25 on page 107 before starting drive. Check setscrew
torque and belt tension after 24 hours of service.

Figure 105: Sheave Alignment (Adjustable Shown)

Drive Belt Adjustment

General Rules of Tensioning

1 The ideal tension is the lowest tension at which the belt will

not slip under peak load conditions.

2 Check tension frequently during the first 24 – 48 hours of

operation.

3 Over tensioning shortens belt and bearing life.

4 Keep belts free from foreign material which may cause

slippage.

5 Inspect V-belts on a periodic basis. Adjust tension if the

belt is slipping. Do not apply belt dressing. This may
damage the belt and cause early failure.

Tension Measurement Procedure

1 Measure the belt span. See Figure 106.

2 Place belt tension checker squarely on one belt at the center

of the belt span. Apply force to the checker, perpendicular
to the belt span, until the belt deflection equals belt span
distance divided by 64. Determine force applied while in
this position.

3 Compare this force to the values on the drive kit label

found on the fan housing.

96 McQuay IM 893-1

Check, Test, and Start Procedures

B e l t S p a n

D e f l e c t i o n =

B e l t S p a n

6 4

T w o G r o o v e

C

A

B

B

D

E

C

A

D

E

D

C

S i n g l e G r o o v e

K e y " E " p r o j e c t s
t o p r o v i d e a g r i p
f o r r e m o v a l .

D o n o t o p e r a t e
s h e e v e s w i t h f l a n g e
p r o j e c t i n g b e y o n d
t h e h u b e n d .

Figure 106: Drive Belt Adjustment

Mounting and Adjusting Motor Sheaves

Figure 107: VM and VP Variable Pitch Sheaves

Adjusting:

1 Slack off all belt tension by moving the motor toward the

driven shaft until the belts are free from the grooves. For
easiest adjustment, remove the belts.

2 Loosen setscrews B and C in the moving parts of the

sheave and pull out external key E (see Figure 107). This
key projects a small amount to provide a grip for removing.

3 Adjust the sheave pitch diameter for the desired fan speed

by opening the moving parts by half or full turns from
closed position. Do not open more than five full turns for
A belts or six full turns for B belts. Adjust both halves of
two-groove sheaves by the same number of turns from
closed to ensure both grooves have the same pitch diameter.

4 Replace external key E and securely tighten setscrews B

over the key. Tighten setscrews C into the keyway in the
fixed half of the sheave.

5 Put on belts and adjust the belt tension. Do not force belts

over grooves. Loosen the belts by adjusting the motor base

closer to the fan shaft.

6 Be sure that all keys are in place and that all setscrews are

tight before starting the drive. Check the setscrews and belt
tension after 24 hours of service.

VM and VP Variable Pitch Sheaves

Mounting:

1

Mount all sheaves on the motor shaft with setscrew A
toward the motor (see Figure 107).

2 Be sure both the driving and driven sheaves are in

alignment and that the shafts are parallel.

3 Fit internal key D between sheave and shaft and lock

setscrew A securely in place.

LVP Variable Pitch Sheaves

Mounting:

1

For single-groove sheaves, slide the sheave onto the motor
shaft so that the side of the sheave with setscrew A is next
to the motor (see Figure 108 on page 98). For two-groove
sheaves, slide the sheave onto the motor shaft so that the
side of the sheave with setscrew A is away from the motor
(see Figure 108 on page 98).

2 To remove the flange and locking rings:

a Loosen setscrews D.

b Loosen but do not remove capscrews E.

c Remove key F. This key projects a small amount to

provide a grip for removing.

d Rotate the flange counterclockwise until it disengages

the threads on the shaft barrel.

3 Be sure that the driving and driven sheaves are in alignment

and the shafts are parallel. When aligning two-groove
sheaves, allow room between the sheave and motor to get
to capscrews E.

4 Insert key C between the sheave and the shaft and tighten

setscrew A securely.

McQuay IM 893-1 97

Check, Test, and Start Procedures

S e c t i o n A - A S e c t i o n A - A

A

B

C

D

E

F

D

E

A

E

C

F

D

A

A

Adjusting:

1 Slack off all belt tension by moving the motor toward the

driven shaft until the belts are free from the grooves. For
easiest adjustment, remove the belts.

2 Loosen setscrews D.

3 Loosen but do not remove capscrews E.

4 Remove key F. This key projects a small amount to provide

a grip for removing.

5 Adjust the pitch diameter by opening or closing the

movable flange by half or full turns. Note that two-groove
sheaves are supplied with both grooves set at the same
pitch diameter. To ensure the same pitch diameter for

satisfactory operation, move both movable flanges the
same number of turns. Do not open sheaves more than
five turns for A belts or six turns for B belts.

6 Replace key F.

7 Tighten setscrews D and capscrews E.

8 Put on the belts and adjust the belt tension. Do not force

belts over grooves. Loosen the belts by adjusting the motor
base closer to the fan shaft

9 Before starting the drive, make sure that all keys are in

place and all setscrews and all capscrews are tight. Check
and retighten all screws and retension the belts after
approximately 24 hours of operation.

MVP Variable Pitch Sheaves

Adjusting:

1

Slack off belt tension by moving the motor toward the
driven shaft until the belts are free from the grooves. For
easiest adjustment, remove the belts.

2 Loosen both locking screws A in outer locking ring, but do

not remove them from the sheave. There is a gap of

approximately 1/2" (1 mm) between the inner and outer
locking rings. This gap must be maintained for satisfactory
locking of the sheave.
If locking screws A are removed by accident and the gap is
lost, screw the outer locking ring down until it touches the
inner locking ring. Then back off the outer ring 1/2 to
3/4 turn until the inner and outer ring screw holes line up.
Reinsert locking screws A, but do not tighten them until
after adjustment is made.

3 Adjust the sheave to the desired pitch diameter by turning

the outer locking ring with a spanner wrench. Any pitch
diameter can be obtained within the sheave range. One
complete turn of the outer locking ring will result in a

0.233" (6 mm) change in pitch diameter.] Do not open

A–B sheaves more than four 3/4 turns for A belts or 6
turns for B belts. Do not open C sheaves more than nine
1/2 turns.

4 Tighten both locking screws A in the outer locking ring.

5 Put on the belts and adjust the belt tension. Do not force

belts over grooves. Loosen the belts by adjusting the motor
base closer to the fan shaft.

CAUTION

Do not loosen any screws other than the two locking screws (A)
in the outer locking ring. Before operating the drive, securely
tighten these screws.

Figure 108: LVP Variable Pitch Sleeves

98 McQuay IM 893-1

Figure 109: MVP Variable Pitch Sheaves (Type A-B)

C e n t e r F l a n g e s

G a p

O u t e r L o c k i n g
R i n g

L o c k i n g

S c r e w s

" A "

3 C a p s c r e w s " B "

I n n e r L o c k i n g
R i n g

S p a n n e r W r e n c h
H o l e

2 L o c k i n g

S c r e w s

" A "

E n d F l a n g e

C e n t e r F l a n g e

A s s e m b l y

T h r e a d

B a r r e l

B a r r e l F l a n g e

1 8 °

S h o r t K e y

H e r e

L o n g K e y

H e r e

Figure 110: MVP Variable Pitch Sheaves (Type A–B)

Check, Test, and Start Procedures

McQuay IM 893-1 99

Final Control Settings

Final Control Settings

When all start-up procedures are completed, set the controls
and program the MicroTech III controller for normal
operation. Use the following list as a guide; some items may
not apply to your unit. For more detail, see IM 919 and OM

920.

1 Turn system switch S1 to ON and S7 to AUTO.

2 Turn gas furnace switch S3 to AUTO or turn electric heat

switch HS1 to ON.

3 Set the electromechanical (Honeywell H205) enthalpy

control (OAE) as required (A, B, C, or D). Set the
solid-state (Honeywell H705/C7400) enthalpy control
(OAE/ RAE) past D.

4 Set the heating and cooling parameters as required for

normal unit operation:

a Temperature \ Zone Cooling \

b Temperature \ Zone Heating \

c Temperature \ Discharge Cooling \

d Temperature \ Discharge Heating \

5 Set the low ambient compressor lockout setpoint as

required in menu, Temperature \ Zone Cooling \ OAT Clg
Lock=. Do not set it below 50°F (10°C) unless the unit is

equipped for low ambient operation.

6 Set the high ambient heat lockout temperature setpoint,

Temperature \ Zone Heating \ OAT Htg Lock= as required.

7 Set the alarm limits as required in

Setup/Service \ Alarm Limits \.

8 Set the compressor lead/lag function as desired using

keypad menu Setup/Service \ Compressor Setup \ Lead
Circuit= and Setup/Service \ Compressor Setup \
Comp Ctrl=. Refer to “Compressor Staging” in IM 919 and

OM 920.

9 Set the duct static pressure control parameters as required

in keypad menu Airflow \ Duct Pressure \.

10 Set the building static pressure control parameters as

required in keypad menu Airflow \ Bldg Pressure \.

11 Set the fan tracking parameters as required in keypad

menus Setup/Service \ Fan Tracking Setup \ and Setup/
Service \ Fan Balance \.

12 Set the economizer control parameters as required in

keypad menu Temperature \ OA Damper \.

13 Set the control timers as required in keypad menu

Setup/Service \ Timer Settings \.

14 Set the date and time in keypad menu

Setup/Service \ Time/Date \.

15 Set the operating schedule as required using keypad menus.

Note: When used with a Building Automation System,
these settings may need to be kept at the default of no
schedule:

a Schedules \ Daily Schedule \

b Schedules \ Holiday Schedule \

16 Temporarily disconnect static pressure sensor tubing from

sensors SPS1 and SPS2 (if installed) and place the unit into
the calibrate mode by using the keypad menu Setup/Service
\ Unit Configuration \ Calibrate Mode= and changing the
value from NO to YES. The calibrate mode automatically
zeroes all static pressure sensors and calibrates any actuator
feedback pots connected to the MicroTech III controller.
When the calibration is finished, the keypad menu System

Summary \ System \ Unit Status= changes from Calib to Off
Man.

17 To restart the unit, reconnect static pressure tubing and

change keypad menu System Summary \ System \ Ctrl
Mode= from OFF to AUTO.

CAUTION

If the unit has hot gas bypass on circuit #1 only, lead circuit
must always be #1.

100 McQuay IM 893-1