Carrier 50FK, JK034-074, 48FK User Manual

Controls Operation,

and Troubleshooting

CONTENTS

Page

SAFETY CONSIDERATIONS .....................2

GENERAL ...................................2-13

Rooftop Information ............................2

VAV Control System ...........................2

Processor Board ..............................2

• P1 — SUPPLY-AIR SET POINT

• P2 — ECONOMIZER POSITION

• P3 — RESET LIMIT

• P4 — DEMAND LIMIT

• P5 — ECONOMIZER MINIMUM POSITION

• P6 — WARM-UP SET POINT

• P7 — SASP RESET TEMPERATURE

• PROCESSOR BOARD OUTPUTS

• CONFIGURATION HEADER AND DIP SWITCH

ASSEMBLY

Relay Board

Display Board .................................5

Thermistors ...................................5

• T1 — SUPPLY-AIR TEMPERATURE THERMISTOR

• T2 — RETURN-AIR TEMPERATURE THERMISTOR

• T3 — SATURATED CONDENSING TEMPERATURE,

CIRCUIT 1

• T4 — SATURATED CONDENSING TEMPERATURE,

CIRCUIT 2

• T10 — RESET TEMPERATURE

Compressor Operation

• CONTROL RELAY (CR)

Accessory Board

• P3 — RESET LIMIT

• P5 — ECONOMIZER MINIMUM POSITION

• P6 — MORNING WARM-UP TEMPERATURE

Single-Step Demand Unit

Demand Limit Control Module (DLCM) ............7

Economizer ..................................10

• ENTHALPY CONTROL

• DIFFERENTIAL ENTHALPY

Variable Frequency Drive (VFD)

Temperature Reset ............................12

CONTROLS INSTALLATION ...................13-25

Control Wiring ...............................13

• NIGHT SETBACK THERMOSTAT

• SPACE TEMPERATURE RESET ACCESSORY

(50DJ900021)

Space Temperature Reset

• INSTALLATION

• CONFIGURATION

• OPERATING SEQUENCE

Demand Limit

• SINGLE-STEP DEMAND LIMIT

• TWO-STEP DEMAND LIMIT

• INSTALLATION

• CONFIGURATION

• OPERATING SEQUENCE

Control From Remote Building Management

System (BMS)

• OCCUPIED/UNOCCUPIED

..................................5

.........................7

..............................7

.......................7

.................12

......................13

................................18

..............................19

48FK,JK034-074

50FK,FY,JK,JY034-104

Variable-Air Volume Rooftop Units

• NIGHT SETBACK CONTROL

• UNIT SUPPLY AIR SET POINT ADJUSTMENT

• DEMAND UNIT (1-STAGE OR 2-STAGE)

• SUPPLY DUCT PRESSURE SET POINT ADJUSTMENT

• EXTERNAL ALARM SIGNAL

• REMOTE ECONOMIZER CONTROL

Smoke Control Modes

.........................21

• FIRE SHUTDOWN MODE

• PRESSURIZATION MODE

• EVACUATION MODE

• SMOKE PURGE MODE

• INSTALLATION

• CONFIGURATION

• OPERATING SEQUENCE

Air Pressure Tubing

...........................23

• INLET GUIDE VANES

• VARIABLE FREQUENCY DRIVE

• MODULATING POWER EXHAUST

START-UP

Initial Check .................................25

Conﬁguration Header .........................26

DIP Switches .................................26

Adjusting Set Points ..........................27

Potentiometers ...............................27

Supply Fan Control with IGV Option .............28

Supply Fan Control with VFD Option ............28

Modulating Power Exhaust

(Option or Accessory) .......................30

START UNIT ................................31-34

Quick Test Program ...........................31

OPERATING INFORMATION ...................34-43

Digital Display ...............................34

CODES 0 THROUGH 8, CAPACITY STEPS

•

.................................25-30

• CODES 20 THROUGH 30 AND 88, OPERATIONAL

STATUS

• CODES 51 THROUGH 87, DIAGNOSTIC

INFORMATION

Operating Sequence

..........................35

• SIZE 034, 038 AND 048-088 UNITS

• SIZE 044 UNITS

• SIZE 104 UNITS

Head Pressure Control

Supply Fan Control with IGV ...................38

Supply Fan Control with VFD ...................38

Modulating Power Exhaust (Option or

Accessory Except FY,JY Units) ...............38

Unit Staging .................................38

TROUBLESHOOTING ........................44-57

Checking Display Codes .......................44

Complete Unit Stoppage .......................44

Single Circuit Stoppage .......................44

Restart Procedure ............................44

Diagnostic Codes .............................45

CODES 51, 52, 55, 56: COMPRESSOR FAILURE

•

........................36

Page

Manufacturer reserves the right to discontinue, or change at any time, speciﬁcations or designs without notice and without incurring obligations.

Book 1 1 Tab 1a 1b

PC 111 Catalog No. 534-716 Printed in U.S.A. Form 48/50F,J-1T Pg 1 4-99 Replaces: 48/50D,F,J-1T

CONTENTS (cont)

Page

CODES 59 AND 60: LOW-PRESSURE SWITCH

•

• CODES 63 AND 64: OIL PRESSURE SWITCH

• CODE 70: ILLEGAL UNIT CONFIGURATION

• CODES 71 TO 76: THERMISTOR/RESISTOR

FAILURE

• CODE 81: RESET THERMISTOR OR

POTENTIOMETER FAILURE

• CODE 82: LEAVING-AIR TEMPERATURE SET POINT

POTENTIOMETER FAILURE

• CODE 83: ECONOMIZER FEEDBACK

POTENTIOMETER FAILURE

• CODE 84: RESET LIMIT POTENTIOMETER

FAILURE

• CODE 85: DEMAND LIMIT POTENTIOMETER (P4)

FAILURE

• CODE 86: MINIMUM POSITION ECONOMIZER

POTENTIOMETER FAILURE

• CODE 87: WARM-UP TEMPERATURE SET POINT

FAILURE

Thermistor Troubleshooting

Electronic Controls Checkout ..................47

....................47

• PROCESSOR BOARD CHECKOUT

• RELAY BOARD TROUBLESHOOTING

• DISPLAY BOARD CHECKOUT

• ACCESSORY BOARD CHECKOUT

• TWO-STEP DEMAND LIMIT CONTROL MODULE

(DLCM) TROUBLESHOOTING

Enthalpy Sensor Checkout

Economizer Motor ............................52

Variable Frequency Drive ......................52

.....................51

• STANDARD TRANSDUCER CONTROL

• EXTERNAL SIGNAL CONTROL

• SUPPLY FAN MOTOR OVERLOAD PROTECTION

VFD Operation

VFD Operational Status ........................54

Restoring Factory VFD Defaults ................54

Unit Wiring ..................................54

START-UP CHECKLIST ..................CL-1, CL-2

...............................54

SAFETY CONSIDERATIONS

Installing, starting up, and servicing this equipment can be hazardous due to system pressures, electrical components; and equipment location (roof, elevated structures, etc.). Only trained, qualiﬁed installers and service mechanics should install, start up, and service this equipment.

When working on this equipment, observe precautions in the literature; on tags, stickers, and labels attached to the equipment, and any other safety precautions that apply. Follow all safety codes. Wear safety glasses and work gloves. Use care in handling, rigging, and setting this equipment, and in handling all electrical components.

Electrical shock can cause personal injury and death. Shut off all power to this equipment during installation and service. There may be more than one disconnect switch. Tag all disconnect locations to alert others not to restore power until work is completed.

GENERAL

IMPORTANT: This literature contains controls, operation, and troubleshooting data for 48FK,JK and 50FK,FY,JK,JY variable air volume rooftop units. Use this guide in conjunction with the separate Installation Instructions literature packaged with the unit.

Carrier 48FK,JK and 50FK,FY,JK,JY units provide ventilation, cooling, and heating (when equipped) in Variable Air Volume (VAV) applications. These units contain factoryinstalled controls which provide full system management. The unit controls also perform self diagnostic tests at unit start-up, monitor operation of the unit, and provide alarms. Information on system operation and status are sent to the central processors by various sensors that are located at the unit and in the conditioned space. Each unit is equipped with a display board.

Rooftop Information — The rooftop controls cycle

supply-fan motor, compressors, and unloaders to maintain the proper temperature conditions. The controls also cycle condenser fans to maintain suitable head pressure. Safeties are continuously monitored to prevent the unit from operating under abnormal conditions. The controls provide control of economizer and cycle or control heating as required.

The controls also allow the service person to operate a ‘quick test’so that all the controlled components can be checked for proper operation.

IMPORTANT:The ﬁeld-supplied and installed switch (or timeclock) MUST BE CLOSED to put unit into the Occupied mode. Unit WILLNOT START until this is accomplished. See base unit installation instructions literature for details.

VAV Control System — The 30 to 100-ton VAV roof-

top units contain a microprocessor-based electronic control system that controls and monitors the rooftop unit functions.

TheVAV control system is composed of several components:

• processor board

• relay board

• display board

• thermistors

• compressor operation feedback (control relay)

• accessory board

• temperature reset package*

• single-step demand limit*

• two-step demand limit control module* *Field-installed accessories.

The VAV control system monitors and controls the following functions of the rooftop unit:

• supply-air temperature (unit capacity)

• morning warm-up or electric heat (if equipped)

• head pressure control, fan cycling

• economizer position

• diagnostic display

• unit check-out (quick test)

• supply air temperature reset (if equipped)

• demand limiting (if equipped)

This unit uses a microprocessor-based electronic control system. Do not use jumpers or other tools to short out components, or to bypass or otherwise depart from recommended procedures. Any short-to-ground of the control board or accompanying wiring may destroy the electronic modules or electrical components.

Processor Board — The processor board, shown in

Fig. 1, contains the logic and the necessary hardware to drive the outputs and the display board. The processor board is enclosed by a sheet metal cover and a heater. The heater is controlled by a thermostat to keep the processor temperature above 32 F (0° C). All electrical connections are made to the processor board through wire and ribbon cables.

LEGEND

DIP — Dual In-Line Package EPROM — Erasable, Programmable Read-Only Memory EXV — Electronic Expansion Valve

Do not remove label covering EPROM. Removal causes program to be erased.

Fig. 1 — Processor Board

*EPROM HT204485-1-XX where ‘‘XX’’ is the current revision

number.

NOTE: Processor Board is positioned in unit with J3 and J10 connections at the bottom.

Several temperature inputs are connected to the processor. There are either 4 or 5 thermistors (depending on the ﬁeld-installed accessories) which input temperature data into the processor through pin terminal connector J1. See Table 1 and Fig. 2.

Several status switches are also monitored. These switches are connected to the processor at pin terminal connector J2. See Fig. 3 and Table 2.

Table 1 — Pin Terminal Connector J1

Thermistor Inputs

CONNECTOR J1

TERMINAL NO.

1,2 Reset Temperature* T10

14,15

16,17 18,19 Return-Air Temperature T2

20,21 Supply-Air Temperature T1

LEGEND

T—Thermistor

*If equipped with accessory temperature reset package.

NOTE: Terminal numbers 3-13 are not used on these units.

TEMPERATURE

INPUT

Saturated Condensing

Temp., Circuit 2

Saturated Condensing

Temp., Circuit 1

UNIT SIZE

034-104

T4 T3

In addition to the unit status switch inputs, the processor board also accepts inputs from several potentiometers. These potentiometers control various operational characteristics of the system. Inputs are received by the processor through pin terminal connector J3. See Fig. 4.

All of the potentiometers must be set before the unit is started in order for the unit to function properly. See StartUp, Potentiometers section on page 28 for information on establishing set points. Each of the potentiometers has a valid range that is used by the control. The valid range is deﬁned as the potentiometer’s resistance value that the control will not consider to be in error. This is usually between 10% and 90% of the potentiometer’s total resistance. The control has been programmed to accept an operational range for the potentiometer, which may not be the same as the valid range.

LEGEND

T—Thermistor

Field Wiring Accessory

Fig. 2 — Pin Terminal Connector J1

Thermistor Inputs

LEGEND

CR — Control Relay EC — Enthalpy Control LPS — Low-Pressure Switch

Fig. 3 — Pin Terminal Connector J2

Status Switch Inputs

Table 2 — Pin Terminal Connector J2

Status Switch Inputs

CONNECTOR J2

TERMINAL NO.

1,2

3,4

7,8

9,10

13,14

15,20

15,24

LEGEND

CR — Control Relay EC — Enthalpy Control LPS — Low-Pressure Switch

NOTE: Terminal numbers 5, 6, 11,12, 16-19, and 21-23 are not used

on these units.

STATUS SWITCH

Oil Pressure,

Circuit 2

Oil Pressure,

Circuit 1

Loss Of Charge,

Circuit 2

Loss of Charge,

Circuit 1

Economizer

Changeover

Compressor Fault

Signal

Compressor Fault

Signal

UNIT SIZE

034-104

Jumpered

LPS2 LPS1

EC CR2 CR1

LEGEND

IN — Input P—Potentiometer Field Wiring RNT — Return Accessory SW — Switch

Factory Wiring

Fig. 4 — Pin Terminal Connector J3

Potentiometer Inputs

The potentiometer locations and functions are as follows:

P1 — SUPPLY-AIR SET POINT — This potentiometer is located on the display board. The supply-air set point is the cooling mode control temperature which the VAV control system will attempt to maintain at Thermistor T1 by control of economizer position and/or cycling unloaders and compressors.

P2 — ECONOMIZER POSITION — Economizer feedback potentiometer is located on the economizer motor.The microprocessor is programmed to indicate an alarm if the travel during initialization is less than 10% of the total potentiometer’s resistance. An alarm condition will also be signaled if the potentiometer fails during operation, indicating that the damper blades are stuck. If either situation occurs, the processor will try to drive the economizer dampers closed.

P3 — RESET LIMIT — This potentiometer is located on the accessory board (provided standard from the factory) in the unit main control box and establishes the maximum amount of reset that can be applied to the supply-air set point (P1). Reset is limited by the P1 default of 70 F. This potentiometer is used only when accessory, ﬁeld-installed temperature reset is used. If temperature reset is used, DIP (dual, in-line package) switch 2 must be in the ON position.

P4 — DEMAND LIMIT — This potentiometer is located near TRAN4 in the unit control box. The demand limit potentiometer is used only if accessory, ﬁeld-installed demand limit is used, and if DIP switch 5 is in the ON position. For single-step demand limit, a ﬁeld-installed 5 to 20 Kohm potentiometer and switch must be used.

P5 — ECONOMIZER MINIMUM POSITION — This potentiometer is on the accessory board (provided standard from the factory) located in the unit main control box. This potentiometer speciﬁes the minimum opening position for the optional economizer. If a fault condition is detected by the processor,an alarm condition will be signaled and the economizer dampers will close.

P6 — WARM-UP SET POINT — This potentiometer is on the accessory board (provided standard from the factory) located in the unit main control box. This potentiometer establishes the set point temperature for the Morning Warm-Up function. When the temperature is reached, Morning Warm-Up is terminated and VAV operation begins. DIP switch 4 must be in the ON position if morning warm-up heat is to be used.

P7 — SASP (SUPPLY AIR SET POINT) RESET TEMPERATURE — This 10 Kohm potentiometer is used only if the accessory, ﬁeld-installed temperature reset package is installed.This potentiometer determines the temperature at which reset will begin. It is located on the accessory temperature reset board. DIP switch 2 must be in the ON position to enable SASP reset.

PROCESSOR BOARD OUTPUTS — The processor board also controls outputs through the relay board. The relay board plugs into the processor board using a ribbon cable.

In addition, the processor board controls the display board. The display board is connected to the processor board by a ribbon cable, and has an LED (light-emitting diode) display showing the status of the unit and diagnostic information.

CONFIGURATION HEADERAND DIP SWITCHASSEMBLY — The processor board is programmed to control a variety of air conditioning units. To tailor the processor to the particular unit being controlled, 2 devices are used. One is the conﬁguration header, and the other is the DIP switch assembly.

The conﬁguration header (part no. 30GB660001) is a series of 8 small wires that are broken or unbroken in a pattern to indicate several unique characteristics of the unit. The conﬁguration header is factory set and should not be changed. Changing the factory setting may cause the unit to malfunction.

The DIP switches conﬁgure the unit for several ﬁeldinstalled options, as well as for several other options that may be unique to the unit. The DIP switches are located under a plastic enclosure which must be removed for access. The switches can be ﬁeld adjusted, but must be adjusted only when the unit control circuit breaker is off.

Relay Board — The relay board is used to control 24-v

and 115-v loads. See Fig. 5. The relay board is connected to the processor board by a ribbon cable at pin J9. Electrical connections to the relay board are made through pins J5 (115 v) and J6 (24 v). The relay board has eight 24-v relays and ﬁve 115-v relays. See Table 3.

Display Board — The display board is located in the

main unit control box and is connected to the J10 port of the processor board through a ribbon cable. The display board contains the supply-air set point potentiometer P1; a 2-digit, LED display; and the display button (see Fig. 6). The LED display is used to convey the operating information and operational error codes.

Thermistors — The processor uses up to 5 thermistors

to sense the temperatures at various points in the system. See Table 1 and Fig. 7-14. All the thermistors have identical temperature versus resistance and voltage drop characteristics, and are monitored by the processor for a short or open circuit. The valid range for a thermistor is 362,640 to 219 ohms. Thermistor details and locations are as follows:

T1 — SUPPLY-AIR TEMPERATURE THERMISTOR — This thermistor is located in the unit supply fan discharge. It provides information for the processor to stage the number of capacity steps required to maintain a desired supplyair temperature.

T2 — RETURN-AIR TEMPERATURE THERMISTOR — This thermistor is located in the mixed-air portion of the unit cabinet. The thermistor’sprimary function is to provide morning warm-up information. This sensor will also provide differential information for the processor during cooling operation (such as the rate of change for a capacity step).

T3 — SATURATEDCONDENSINGTEMPERATURE, CIRCUIT 1 — This thermistor is located on the condenser coil return bend. See Fig. 13 and 14. It controls the staging of the unit condenser fans based on the condensing temperature of the refrigerant at the designated position on the condenser coil.

T4 — SATURATEDCONDENSINGTEMPERATURE, CIRCUIT 2 — This thermistor is located on the condenser coil return bend. See Fig. 13 and 14. It controls the staging of the unit condenser fans based on the condensing temperature of the refrigerant at the designated position on the condenser coil.

T10 — RESET TEMPERATURE — This thermistor is used only if the accessory temperature reset package is used. It provides occupied space temperature information to the processor, which determines whether or not reset is required. The thermistor is remotely mounted outside the unit in the conditioned space.

Table 3 — Output Pin and Terminal Assignments

OUTPUT PIN-

TERMINAL

J6-1

J6-2

J6-3

J6-4

J6-5

J6-6 J6-7 Economizer Open Relay (K7) EOR

J6-8 Economizer Close Relay (K8) ECR J5-1 Supply Fan Relay (K9) J5-2 Morning Warm-Up Relay (K10) HIR

J5-3

J5-4 J5-5 External Alarm Relay (K13) ALM

LEGEND

ALM — Alarm CR — Control Relay ECR — Economizer Close Relay EOR — Economizer Open Relay HIR — Heat Interlock Relay IFC — Indoor (Evaporator) Fan Contactor OFC — Outdoor (Condenser) Fan Contactor U—Unloader

Stage 1 Compressor Relay (K1)*

Stage 2 Compressor Relay (K2)*

Stage 3 Compressor Relay (K3)*

Stage 4 Compressor Relay (K4)†

Stage 5 Compressor Relay (K5)†

Stage 6 Compressor Relay (K6)†

Stage 1 Condenser Fan Relay (K11)

Stage 2 Condenser Fan Relay (K12)

NAME RATING DEVICE

CR1 U2**

24 vac

115 vac

*Circuit 1.

†Circuit 2.

**U2 is not used on 044 units.

††OFC2 on 034-048 units; OFC3 on 054-104 units.

\ Used on 054-104 units only.

Not Used

CR2

Not Used

IFC

OFC2/OFC3 ††

OFC4 \

LEGEND

CR — Control Relay J—Terminal Pin Connectors K—Relay

Fig. 5 — Relay Board

P1 SUPPLY AIR SET POINT POTENTIOMETER

TWO-DIGIT DISPLAY

DISPLAY BUTTON

Fig. 6 — Display/Set Point Board

Compressor Operation

CONTROL RELAY (CR) — This relay provides information to the processor about compressor operation (one control relay per compressor). The relay controls and protects the compressor and also controls the crankcase heater.

A control signal to check the safety statuses and to start the compressor is sent from the relay board. This signal travels through all of the safeties: the high-pressure switch, and the internal protector (where used) and on to the control relay coil. Once the control relay coil has been energized, the control relay completes a feedback circuit for the processor, informs the processor of the status of the compressor safeties, energizes the compressor contactor coil, and deenergizes the crankcase heaters. A fault will be detected by the processor if the control relay opens during operation or startup. The processor will lock the compressor or the circuit off by deenergizing the appropriate relay(s) on the relay board and energizing an alarm signal.

Accessory Board — The accessory board is standard

(factory supplied) in the VAV rooftop units. See Fig. 15. This board is located in the control box of each unit. Each board has a prewired connector supplied with it to connect directly to the processor board. It has 3 potentiometers: P3, P5, and P6.

P3 — RESET LIMIT — The processor board is programmed for occupied space temperature reset. In order for reset to work, the accessory temperature reset board must be used. Potentiometer P3 is the maximum set point temperature to which the supply air can be reset.

P5 — ECONOMIZER MINIMUM POSITION — This potentiometer controls the set point for the minimum position of the economizer.

P6 — MORNING WARM-UP TEMPERATURE—This potentiometer controls the morning warm-up temperature set point.

Single-Step Demand Limit — The single step de-

mand limit provides a means to limit the capacity of the V AV unit using an external switch. Single step demand limit will limit the compressor displacement based on the ratio of the wiper arm to the full scale resistance. The exact percentage of capacity reduction differsdepending on the number of capacity steps.

A3-wire, 5 to 20 Kohm, ﬁeld-supplied potentiometer (P4) is required for this option. The potentiometer should be wired to the processor J3 connections. In order to control the demand limit, the wiper arm of the potentiometer should be switched open and closed based on the demand limit requirement. The control switch is also ﬁeld-supplied and installed.

If the wiper arm wire is open, all capacity stages can be used. When the wiper arm wire is closed, the capacity is reduced by the amount set on potentiometer P4.

Demand Limit Control Module (DLCM) — The

DLCM provides a 2-step demand limit control using an external switch. The ﬁrst step is between 50% and 100% of the maximum compressor displacement. See Fig. 16. The second step is between 0% and 49% of the maximum compressor displacement. The exact percentage differs depending on the number of capacity steps.

Two adjustable potentiometers are used to set the 2 demand limit points. Potentiometer P1 is used to set a demand limit between 50% and 100% of the unit capacity. Potentiometer P2 is used to set a demand limit between 0% and 49% of unit capacity.

If no power is supplied to the demand limit control module, all capacity stages can be used. When power is supplied to terminal IN1 only, the ﬁrst step of the demand limit control is energized and the capacity is reduced by the amount set on potentiometer P1. When power is supplied to terminal IN2 only,or to both IN1 and IN2, the capacity is reduced by the amount set on potentiometer P2.

GAS SECTION HORIZONTAL SUPPLY SECTION

(48FK,JK ONLY) (50FY,JY ONLY) AND EXTENDED

PLENUM SECTION (50FKX,FKY,JKX,JKY)

Fig. 7 — Thermistor T1 Location, 48FK,JK, 50FY,JY and 50FKX,FKY,JKX,JKY 034-048 Units

FAN DISCHARGE/ELECTRIC HEAT SECTION

Fig. 8 — Thermistor T1 Location, 50FK,JK034-048 Units

GAS SECTION HORIZONTAL DISCHARGE SECTION (50FY,JY)

(48FK,JK) AND EXTENDED

PLENUM SECTION (50FKX,FKY,JKX,JKY)

Fig. 9 — Thermistor T1 Location, 48FK,JK, 50JY and

50JKX,JKY 054-074 Units and 50FKX,FKY and 50FY054-104 Units

FAN DISCHARGE/ELECTRIC HEAT SECTION

Fig. 10 — Thermistor T1 Location, 50FK,JK054-074 Units

STANDARD

FILTERS

BAG

FILTERS

Fig. 11— Thermistor T2 Location, Size 034-048 Units

STANDARD FILTERS BAG FILTERS

(054-074 Only)

Fig. 12 — Thermistor T2 Location, Size 054-104 Units

Economizer — Economizer control is used to control

the outside and return air dampers of the unit, to satisfy space cooling demand using all outside air (when permitted), and to satisfy cooling in conjunction with compressor operation (when conditions permit). During Occupied periods without cooling demand, the outside-air dampers will be at the userconﬁgured Minimum Damper Position (at P5 on accessory board). During Unoccupied periods, the outside-air dampers will be closed.

The economizer is available as a factory-installed option. The user can install an accessory differentialenthalpy sensor to enhance economizer control. Refer to the installation section for ﬁeld wiring of the sensor.

Fig. 13 — Thermistor T3 and T4 Locations,

Size 034-048 Units

ENTHALPY CONTROL — Outside air enthalpy control is standard with the factory-installed economizer option. Enthalpy is sensed by a controller located behind the end outside air hood. The control can be accessed by removing the upper hood ﬁlter. See Fig. 17.

DIFFERENTIALENTHALPY— Added efficienciesin economizer control can be gained by installing a differential enthalpy sensor in the return air duct. When differential enthalpy control is installed, the economizer control will use the air stream with lower enthalpy (outside air or return air) to provide for lower compressor operating costs during integrated economizer cycle operation. The differential enthalpy sensor is installed in the return-air duct.

054 UNITS

064, 074, 078 UNITS

088, 104 UNITS

Fig. 14 — Thermistor T3 and T4 Locations, Size 054-104 Units

LEGEND

ECON — Economizer MIN — Minimum P—Potentiometer VAV — Variable-Air Volume

Fig. 15 — Accessory Relay Board

(Standard; Factory Supplied)

Variable Frequency Drive (VFD) — The optional

VFD is used to modulate supply fan airﬂow to maintain duct static pressure on VAV applications. The VFD is located in the supply fan section (see Fig. 18 and 19), and can be accessed by opening the fan section access door.

The unit is supplied with a pressure transducer capable of measuring from 0.0 to 5.0 in. wg. The pressure transducer will senda4to20mAsignal to the VFD to modulate the speed of the indoor fan motor to precisely control the fan to the desired static pressure set point. The VFD is factory set at 2.5 in. wg duct static pressure. Refer to the Operating Sequence section for more information on the VFD.

The VFD has been programmed and wired at the factory for this application. No further adjustments (except for Duct Static Pressure Set Point) should be necessary at start-up. Factory jumper wire conﬁgurations are shown in the Supply Fan Control with VFD Option section on page 28.

A separate service manual for the factory-installed VFD is supplied with each unit. Refer to the VFD manual for more information on the VFD controls.

Temperature Reset — Accessory temperature reset al-

lows the unit to automatically adjust (‘‘reset’’) the supplyair temperature set point to a higher value once most of the space cooling load has been met. When the space conditions are satisﬁed, the VAV terminals will close to the minimum position.All VAV units will sense the decrease in actual supplyair temperature and the unit controls respond by reducing

LEGEND

IC — Integrated Circuit IN — Input P—Potentiometer RTN — Return

Fig. 16 — Two-Step Demand Limit Module

Fig. 17 — Enthalpy Sensor Location

Fig. 18 — Variable Frequency Drive,

Sizes 034-048 and 078-104

Fig. 19 — Variable Frequency Drive, Sizes 054-074

capacity stages to maintain user-established supply-air set point temperature. When VAV units are also equipped with optional supply duct pressure controls (either inlet guide vanes [IGV] or variable frequency drive package), the unit also senses an increase in duct static pressure and responds by closing IGV dampers or slowing fan wheel speed to maintain userconﬁgured set points for supply duct pressure. Allowing the supply-air temperature to be reset to a higher value maintains air circulation in the space without costly overcooling.

The accessory package is required for temperature reset.

The accessory includes:

• thermistor T10, to monitor space temperature

• reset temperature potentiometer P7, to establish start temperature for reset operation

• reset limit potentiometer P3, to establish maximum level of modiﬁed supply-air temperature

More than one space sensor may be used if an average space temperature is desired for initiating temperature reset. Refer to installation section for sensor part number and wiring schematic.

Temperature reset will start when space temperature (at T10) drops to the set point at P7. When Temperature Reset is active, the LED (light-emitting diode) display will show

code . Automatic adjustment of supply-air temperature

set point will end when modiﬁed SASP equals reset limit set point at P3. (See formula for automatic modiﬁcation of SASP in Controls Installation, Space Temperature Reset section on this page.)

CONTROLS INSTALLATION

The VAV units may be used in applications with additional control features, options, or accessories. Refer to the appropriate accessory installation instructions for more information on installing that accessory.Unit control box component arrangement is shown in Fig. 20-22. Control options and accessories available for VAV units are:

• smoke control modes

• differential enthalpy sensor

• electric heaters (sizes 034-074 only)

• modulating power exhaust

• Motormastert I control

• space temperature reset

• night setback thermostat (ﬁeld-supplied)

• single step demand limit

• two-step demand limit

• inlet guide vanes

• variable frequency drive

• variable frequency drive remote display kit

Control Wiring — A switch or timeclock (ﬁeld sup-

plied) must be wired in to control when unit will go into and out of Occupied mode. Connect switch or timeclock between terminals 1 and 2 on terminal block 3 (sizes 034-048) or terminal block 4 (sizes 054-104) in unit control box. See Fig. 23. The circuit potential is 24 v.

Variable air volume units equipped with warm-up heat require that room terminals be controlled to go fully open when unit goes into the Heating mode. Heating interlock relay (HIR) is provided for this function. The relay is located in the unit control box. When unit goes into Heating mode, interlock relay is energized providing switch closure or opening (depending on how ﬁeld power source is set up) to open the room terminals. Field connections for interlock relays are terminals 3 and 4 (for normally open contacts) and terminals 3 and 7 (for normally closed contacts) on terminal block 3 (sizes 034-048) or terminals block 4 (sizes 054-104). See Fig. 24. Note that a ﬁeld-supplied power source is required.

There are no required 115-volt ﬁeld wiring connections, therefore no provisions have been made in the unit for running 115-volt wiring. If any of the ﬁeld-installed options requiring 115-volt connections are desired, the unit must be modiﬁed in the ﬁeld for 115-volt wiring.

NIGHT SETBACK THERMOSTAT — Wire ﬁeld-supplied thermostat (suitable for 24-v circuit) between terminals 1 and 2 on terminal block 3 (sizes 034-048) or terminal block 4 (sizes 054-104). This thermostat is used to bypass the timeclock occupied/unoccupied switch and is used to operate unit during unoccupied times at more economical temperatures. (See Fig. 23.)

SPACE TEMPERATURE RESET ACCESSORY (50DJ900021) — Consists of a thermistor (T10) and a reset board with a potentiometer (P7) that is used to set space temperature at which reset starts. Mount reset board in unit control box or other convenient place. Wire thermistor in series with P7 and connect to terminals 12 and 15 on terminal block 3 (sizes 034-048) or terminal block 4 (sizes 054-104) in unit control box. If there is a long run to conditioned space, it is necessary to splice additional wire to thermistor. The reset board has 2 pressure connectors for ﬁeld wiring. (See Fig. 25).

Space Temperature Reset

INSTALLATION — Install the accessory temperature reset package in accordance with instructions provided with the accessory kit.

Mount the reset board in the unit control box (or other suitable location) per instructions.

Locate the thermistor T10 in a suitable location in the occupied space per instructions.

Wire T10 to the reset board and to the unit control terminal block per Fig. 25. Wire the other terminal on the reset board to the unit control terminal block per Fig. 25.

If multiple sensors are required to average the space temperature, see Fig. 26. Use only Carrier Part Number HH79NZ014 sensor, in arrangements of 4 or 9 sensors, with total wiring not to exceed 1000 ft.

To enable reset function, change DIP (dual in-line package) switch 2 to position ON. (Disconnect control power before changing DIP switch positions; reconnect power after all changes have been made.)

CONFIGURATION — Set points for reset operation are established at potentiometers P7 and P3 (on the reset board).

Potentiometer P7 — Reset temperature set point (temperature at which reset function will start). Maximum of 80 F, minimum 0° F .Set below normal room cooling set point level to sense overcooling in the occupied space.

NOTE: It is difficult to accurately set the P7 potentiometer to the desired set point. Use the procedure below.

Proper setting of the P7 potentiometer may be made on a resistance basis. The microprocessor initiates reset when it detects a resistance of the thermistor plus the potentiometer of 13,084 ohm. The potentiometer set point may be calculated using the following formula:

= 13,084 – T10

Where: P7

= the desired set point of the P7 potentiometer in ohms

T10R= the resistance of the T10 thermistor for the desired

set point

Fig. 20 — Unit Control Box Arrangement, Sizes 034-04814Fig. 21 — Unit Control Box Arrangement, Sizes 054-078

Fig. 22 — Unit Control Box Arrangement, Sizes 088 and 104

034-048: TB3 054-104: TB4

Control will automatically adjust leaving air temperature by the following formula:

MSP = SP + [(P3 - SP) / 3] x (P7 − T10) where: MSP = Modiﬁed Leaving-Air Set Point

OCCUPIED/UNOCCUPIED

SWITCH

SP = Supply-Air Set Point P3 = Maximum Supply-Air Temperature (reset limit) P7 = Reset Initiation Temperature (reset set point)

NIGHT SETBACK THERMOSTAT

T10 = Actual Space Temperature 3 = Ratio for reset (F) (ﬁxed parameter)

Table 4 — Thermistor Resistance and

NOTES:

1. Occ/Unocc switch closes when occupied.

2. Night setback thermostat closes when in night setback heating.

Fig. 23 — Occupied/Unoccupied Switch with

Night Setback Thermostat

034-048: TB3 054-104: TB4

N.O.

N.C.

FIELD SUPPLIED POWER SOURCE

SIGNAL TO ROOM TERMINALS

Fig. 24 — Heat Interlock Relay

034-048: TB3 054-104: TB4

T10

RESET BOARD

Fig. 25 — Accessory Reset Board

EXAMPLE: T10 desired set point is 70 F.

from Table 4 for 70 F is 5929 ohms.

T10

P7R= 13,084 – 5929 P7R= 7155 ohms

Using an ohmmeter, set the P7 potentiometer to

7155 ohms to achieve a reset initiation set point of 70 F. Potentiometer P3 — Reset limit set point (maximum tem-

perature value for modiﬁed supply air set point). Maximum of 70 F, minimum 40 F. Set between leaving air set point (P1) and 70 F (maximum range permitted by control).

OPERATING SEQUENCE — If space temperature is above

Voltage Drop Characteristics

TEMP

(F)

31.0 16813.8 3.582

32.0 16345.7 3.553

33.0 15892.2 3.523

34.0 15452.7 3.494

35.0 15026.7 3.464

36.0 14613.9 3.434

37.0 14213.6 3.404

38.0 13825.5 3.373

39.0 13449.2 3.343

40.0 13084.2 3.312

41.0 12730.1 3.281

42.0 12386.6 3.250

43.0 12053.3 3.219

44.0 11730.0 3.187

45.0 11416.1 3.156

46.0 11111.5 3.124

47.0 10815.8 3.093

48.0 10528.7 3.061

49.0 10250.0 3.029

50.0 9979.3 2.997

51.0 9716.5 2.965

52.0 9461.3 2.933

53.0 9213.4 2.901

54.0 8972.6 2.869

55.0 8738.6 2.837

56.0 8511.4 2.805

57.0 8290.6 2.772

58.0 8076.1 2.740

59.0 7867.7 2.708

60.0 7665.1 2.676

61.0 7468.3 2.644

62.0 7277.1 2.612

63.0 7091.2 2.581

64.0 6910.6 2.549

65.0 6735.1 2.517

66.0 6564.4 2.486

67.0 6398.6 2.454

68.0 6237.5 2.423

69.0 6080.8 2.391

70.0 5928.6 2.360

71.0 5780.6 2.329

72.0 5636.8 2.299

73.0 5497.0 2.268

74.0 5361.2 2.237

75.0 5229.1 2.207

76.0 5100.8 2.177

77.0 4976.0 2.147

78.0 4854.8 2.117

79.0 4736.9 2.088

80.0 4622.4 2.058

reset set point (T10 > P7), no reset will occur.

If space temperature is equal to or less that reset set point

(T10 < P7), the LED will display and reset will begin.

RESISTANCE

(Ohms)

VOLTAGE

DROP (v)

SIZES 034-048 TB3

TO ACCESSORY SPACE TEMPERATURE RESET CONTROL BOARD

SIZES 054-104 TB4

SIZES 034-048 TB3

12 15

TO ACCESSORY SPACE

TEMPERATURE RESET

CONTROL BOARD

SIZES 054-104 TB4

12 15

RED BLK

RED

BLK

SENSOR 1 SENSOR 2 SENSOR 3 SENSOR 4

RED BLK

SPACE TEMPERATURE RESET — 4 SENSOR AVERAGING APPLICATION

RED BLK

BLK

SENSOR 1

RED

RED BLK

SENSOR 2

RED BLK

SENSOR 3

RED

BLK

SENSOR 4

NOTE:Sensorpart number is HH79NZ014.

BLK

RED

SPACE TEMPERATURE RESET — 9 SENSOR AVERAGING APPLICATION

Fig. 26 — Space Temperature Sensor Averaging

Demand Limit — The demand limit function provides

a means to limit the cooling capacity of the VAV unit using an external discrete switch function. When enabled by the closure of the external switch, the control will limit the available compressor staging capacity according to user set points established at demand limit potentiometer(s).

The unit controls support two types of demand limit: single-

step and 2-step control. SINGLE-STEPDEMAND LIMIT — This function will limit

the total compressor staging based on the ratio of the set point potentiometer’s wiper arm position to the full scale resistance of the potentiometer.The exact percentage of capacity reduction differs depending on the number of capacity steps.

A ﬁeld-supplied potentiometer and control switch are required for this function. See installation section for speciﬁcation on potentiometer and ﬁeld wiring.

TWO-STEP DEMAND LIMIT — Two-step demand limit is provided with the installation of the accessory Demand Limit

SENSOR 6SENSOR 5

RED BLK

SENSOR 8SENSOR 7 SENSOR 9

RED BLK

Control Module kit plus installation of 2 ﬁeld-supplied control switches (SPST-NO each). This accessory control provides for a ﬁrst step reduction of 50% to 100% of the maximum compressor staging; the second step provides for reduction between 0% and 49%. The exact percentage of capacity reduction differs depending on the number of capacity steps.

When demand limit is active, the LED display will show

code . INSTALLATION

Single-Step Demand Limit — A 3-wire 5 to 20 K-ohm potentiometer must be ﬁeld-supplied and installed. A singlepole normally open switch is also required (ﬁeld-supplied and -installed). Locate the potentiometer (designated P4) and the switch in a suitable location (external from the unit or in the unit control box).

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