McQuay WMC 145SBS - 400DBS Maintenance Manual

Operating & Maintenance Manual

OMM 1008-1

Group: Chiller

Part Number: 332830001

Effective: November 17, 2010

Supersedes: April 2010

Magnitude™ Magnetic Bearing Chillers

Model WMC 145SBS – 400DBS

OITS Software Version: 2.01.01

Control Software Version: WMCU3UU02B

Table of Contents

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

Features of the Control Panel.................4

Definitions ................................................5

General Description.................................8

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

Use with On-Site Generators ............................ 10

Multi-Chiller Setup ...............................10

Operating Limits:.............................................. 12

Operating the Control System..............14

Interface Panel On/Off......................................14

Start/Stop Unit .................................................. 14

Change Setpoints .............................................. 14

Alarms .............................................................. 14

Component Failure ........................................... 15

Component Description ........................15

Operator Interface Touch Screen ...................... 15

Controller Description ...................................... 15

Navigating......................................................... 16

Unit Controller.......................................18

Unit Controller Setpoints .................................. 18

Faults, Problems, Warnings ..............................21

Controller Functions ......................................... 21

Compressor Controller .........................23

Compressor Faults, Problems, Warnings .......... 24

Compressor Control Functions ......................... 25

Compressor On-Board

Controllers..............................................28

VIEW Screens .................................................. 32

SET Screens...................................................... 37

SERVICE Screen .............................................. 50

HISTORY Screens............................................ 51

Download Data ................................................. 52

ACTIVE ALARM Screen.................................53

Unit Controller Menu Screens ............. 55

Menu Matrix ..................................................... 56

Compressor Controller Menu

Screens ................................................... 72

Menu Matrix ..................................................... 72

BAS Interface ........................................ 74

Sequence of Operation ......................... 74

Operating the Chiller Control

System .................................................... 75

Interface Panel On/Off......................................75

Start/Stop Unit .................................................. 75

Change Setpoints .............................................. 76

Alarms............................................................... 76

Interface Panel Failure ...................................... 76

Annual Shutdown ................................. 77

Annual Startup .................................................. 77

Maintenance .......................................... 78

Pressure/Temperature Chart..............................78

Routine Maintenance ........................................78

Repair of System............................................... 79

Maintenance Schedule.......................... 82

Service Programs .................................. 83

Operator Interface Touch

Screen......................................................30

Navigation ........................................................ 30

Screen Descriptions .......................................... 32

Manufactured in an ISO Certified Facility

©2010 McQuay International. Illustrations and data cover the McQuay International product at the time of publication and we reserve
the right to make changes in design and construction at anytime without notice. ™® The following are trademarks or registered
trademarks of their respective companies: BACnet from ASHRAE; LONM
managed, granted and used by LONM
Electric; MicroTech II, and Open Choices from McQuay International.

2 OMM 1008-1

Operator Schools................................... 83

Limited Warranty ................................. 83

ARK

ARK

International under a license granted by Echelon Corporation; Modbus from Schneider

, LonTalk, LONW

ORKS

, and the LONM

ARK

logo are

Introduction

This manual provides setup, operating, and troubleshooting information for McQuay Magnitude™ centrifugal
chillers with the MicroTech ΙΙ® controller. Please refer to the current version of installation manual IM 1029 for
information relating to installing the unit.

!

WARNING

Electric shock hazard. Improper handling of this equipment can cause personal injury or equipment damage. This
equipment must be properly grounded. Connections to and service of the MicroTech II control panel must be performed
only by personnel that are knowledgeable in the operation of the equipment being controlled..

!

CAUTION

Static sensitive components. A static discharge while handling electronic circuit boards can cause damage to the
components. Discharge any static electrical charge by touching the bare metal inside the control panel before performing
any service work. Never unplug any cables, circuit board terminal blocks, or power plugs while power is applied to the
panel.

NOTICE

This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in
accordance with this instruction manual, may cause interference to radio communications. Operation of this
equipment in a residential area is likely to cause harmful interference, in which case the owner will be required to
correct the interference at the owner’s own expense.

McQuay disclaims any liability resulting from any interference or for the correction thereof.

Temperature and humidity considerations

The unit controllers are designed to operate within an ambient temperature range 20°F to 130°F
(-7°C to 54°C) with a maximum relative humidity of 95% (non-condensing). The unit is designed for indoor,
non-freezing locations only.

H

AZARD 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.

OMM 1008-1 3

Features of the Control Panel

• Control of leaving chilled water within a ±0.2°F (±0.1°C) tolerance.

• Display of the following temperatures and pressures on a 15-inch Super VGA touch-screen operator

interface

• Entering and leaving chilled water temperature

• Enter and leaving condenser water temperature

• Saturated evaporator refrigerant temperature and pressure

• Saturated condenser temperature and pressure

• Outside air temperature (optional)

• Suction line, liquid line and discharge line temperatures, calculated superheat for discharge and

suction lines, and calculated sub-cooling for liquid line

• Automatic control of primary and standby evaporator and condenser pumps.

• Control of up to 4 stages of cooling tower fans plus modulating bypass valve and/or tower fan VFD.

Although fan staging is available, continuous, modulated control of tower capacity is preferred and
recommended.

• History trend feature that will constantly log chiller functions and setpoints. The controller will store and

display all accumulated data for recall in a graphic format on the screen. Data can be downloaded for
archival purposes.

• Three levels of security protection against unauthorized changing of setpoints and other control

parameters.

• Plain language warning and fault diagnostics to inform operators of most warning or fault conditions.

Warnings, problems and faults are time and date stamped for identification of when the fault condition
occurred. In addition, the operating conditions that existed just prior to shutdown can be recalled to aid
in resolving the cause of the problem.

• Twenty-five previous faults and related operating conditions are available from the display. Data can be

exported for archival purposes via a 3.5-inch floppy drive or other device (depending on date of
manufacture).

• Soft loading feature reduces electrical consumption and peak demand charges during system loop pull-

down.

• Remote input signals for chilled water reset, demand limiting and unit enable.

• Manual control mode allows the service technician to command the unit to different operating states.

Useful for system checkout.

• BAS communication capability via L

BAS manufacturers.

• Service Test mode for troubleshooting controller outputs.

• Pressure transducers for direct reading of system pressures.

• Preemptive control of low evaporator and high discharge pressure conditions to take corrective action

prior to a fault trip.

ONTALK

, Modbus or BACnet standard open protocols for most

4 OMM 1008-1

Definitions

Active Setpoint

The active setpoint is the parameter setting in effect at any given moment. This variation can occur on
setpoints that can be altered during normal operation. Resetting the chilled water leaving temperature
setpoint by one of several methods such as return water temperature is an example.

Active Capacity Limit

The active capacity setpoint is the setting in effect at any given moment. Any one of several external inputs
can limit a compressor’s capacity below its maximum value.

Active-Amp-Limit

Active amp limit is the actual amp limit imposed by an outside signal such as the load limit function.

Condenser Recirc (Recirculation) Timer

A timing function, with a 30-second default, that holds off any reading of condenser water for the duration of
the timing setting. This delay allows the sensors to take a more accurate reading of the condenser water
temperature.

Dead Band

The dead band is a set of values associated with a setpoint such that a change in the variable occurring within
the dead band causes no action from the controller. For example, if a temperature setpoint is 44°F and it has
a dead band of ± 2.0 degrees F, nothing will happen until the measured temperature is less than 42°F or more
than 46°F.

DIN

Digital input usually followed by a number designating the number of the input.

Discharge Superheat

Discharge superheat is calculated using the following equation:

Discharge Superheat = Discharge Temperature – Condenser Saturated Temperature

Error

In the context of this manual, “Error” is the difference between the actual value of a variable and the target
setting or setpoint.

Evaporator Approach

The evaporator approach is calculated for each circuit. The equation is as follows:

Evaporator Approach = LWT – Evaporator Saturated Temperature

Evap Hold-loading

This is a setpoint that establishes the minimum evaporator pressure to which the chiller is allowed to go. It
signals that the unit is at full load so the no further loading will occur that would lower the pressure even
further.

Evap Recirc (Evaporation Recirculation) Timer

A timing function, with a 30-second default, that holds off any reading of chilled water for the duration of the
timing setting. This delay allows the chilled water sensors to take a more accurate reading of the chilled
water temperature.

EXV

Electronic expansion valve, used to control the flow of refrigerant to the evaporator, controlled by the circuit
microprocessor.

OMM 1008-1 5

Load Limit

An external signal from the keypad, the BAS, or a 4-20 ma signal that limits the compressor loading to a
designated percent of full load. Used to limit unit power input.

Load Balance

Load balance is a technique that equally distributes the total unit load between two or more running
compressors.

Low Pressure Hold (Inhibit) Setpoint

The psi evaporator pressure setting at which the controller will not allow further compressor loading.
“Hold” and “Inhibit” are used interchangeably.

Low Pressure Unload Setpoint

The psi evaporator pressure setting at which the controller will unload the compressor in an effort to
maintain the minimum setting.

LWT

Evaporator leaving water temperature. The “water” is any fluid used in the chiller circuit.

LWT Error

Error in the controller context is the difference between the value of a variable and the setpoint. For
example, if the LWT setpoint is 44°F and the actual temperature of the water at a given moment is 46°F,
the LWT error is +2 degrees.

LWT Slope

The LWT slope is an indication of the trend of the chilled water temperature. It is calculated by taking
readings of the temperature every few seconds and subtracting them from the previous value over a
rolling one-minute interval.

ms

Milli-second

Maximum Saturated Condenser Temperature

The maximum saturated condenser temperature allowed is calculated based on the compressor
operational envelope.

OAT

Outside ambient air temperature

Offset

Offset is the difference between the actual value of a variable (such as temperature or pressure) and the
reading shown on the microprocessor as a result of the sensor signal.

OITS

Operator Interface Touch Screen, one screen per unit provides operating data visually and accommodates
setpoint entry.

pLAN

Peco Local Area Network is the proprietary name of the network connecting the control elements.

Refrigerant Saturated Temperature

Refrigerant saturated temperature is calculated from the pressure sensor readings. The pressure is fitted
to an R-134a temperature/pressure curve to determine the saturated temperature.

Soft Load

Soft Load is a control sub-routine that allows the chiller to load up gradually. It requires setpoint inputs
of selecting it by Yes or No inputs by selecting the percent load to start ramping up and by selecting the
time to ramp up to full load (up to 60 minutes).

6 OMM 1008-1

SP

Setpoint

Suction Superheat

Suction superheat is calculated for each circuit using the following equation:

Suction Superheat = Suction Temperature – Evaporator Saturated Temperature

Stageup/Stagedown Delta-T

Staging is the act of starting or stopping a compressor or fan when another is still operating. Startup and Stop
is the act of starting the first compressor or fan and stopping the last compressor or fan. The Delta-T is the
“dead band” on either side the setpoint in which no action is taken.

Stage Up Delay

The time delay from the start of the first compressor to the start of the second.

Startup Delta-T

Number of degrees above the LWT setpoint required to start the first compressor.

Stop Delta-T

Number of degrees below the LWT setpoint required for the last compressor to stop.

VDC

Volts, Direct Current; sometimes noted as vdc.

VFD

Variable Frequency Drive, a device located on the compressor used to vary the compressor speed.

OMM 1008-1 7

Unit Control

Panel

Panel

(OITS)

Behind Panel

General Description

Major Components

Figure 1, Major Component Location

Evaporator Relief

Valve, Behind Panel

Compressor #1

Compressor #2

Operator
Interface

Condenser
Relief Valves

Power Panel
(Front End Box)

Control Panel

Electronic Expansion Valve

General Description

The centrifugal MicroTech ΙΙ control system consists of a microprocessor-based controller in the control
panel, as well as on-board the compressors, providing monitoring and control functions required for the
controlled, efficient operation of the chiller. The system consists of the following components:

• Operator Interface Touch Screen (OITS), one per unit-provides unit information and is the primary

setpoint input instrument. It has no control function.

• Unit Controller, controls unit functions and communicates with other auxiliaries. It is the secondary

location for setpoint input if, and only if, the OITS is inoperative.

• On-board compressor controller mounted on each compressor that monitors compressor operation and

controls bearing operation.

The operator can monitor all operating conditions by using the unit-mounted OITS. In addition to providing
all normal operating controls, the MicroTech II control system monitors equipment protection devices on the
unit and will take corrective action if the chiller is operating outside of its normal design conditions. If a fault
condition develops, the controller will shut a compressor, or the entire unit, down and activate an alarm
output. Important operating conditions at the time an alarm condition occurs are retained in the controller’s
memory to aid in troubleshooting and fault analysis.

The system is password protected and only allows access by authorized personnel. The operator must enter
the password into the touch screen (or one of the controller's keypad) before any setpoints can be altered.

8 OMM 1008-1

Outside Panel

Controller

Comp #2 I/O

Control Panel

Figure 2, Control Panel

EXV Board

Field Wiring Knockouts

On/Off
Switches
UNIT
COMP #1
COMP #2

Universal

Communication

Module

Emergency

Shutdown Switch,

The unit controller, the OITS microprocessor, the unit and compressor on/off switches and other minor
components are mounted in the control panel. The switches are designated “I” for on and “0” for off. The
compressor on/off switch should only be used when an immediate stop is required since the normal shut
down sequence is bypassed.

The switch panel also has a circuit breaker that interrupts power to the cooling tower fans, valves, and
evaporator and condenser pumps, if any of these are tied into the MicroTech II controller for control of their
operation. If these components operate independently from the chiller control, the breaker has no effect.

The unit controller's function is acquiring and processing data relating to the chiller operation and issueing
instructions to various components to maintain controlled operation. The unit controller also sends
information to the OITS for graphic display. The controller has a 4x20 LCD display and keys for accessing
data and changing setpoints. If the OITS should become inoperable.The controller LCD can display most of
the same information as the OITS and can operate the chiller independently if the OITS is not available.

Terminal Board
TB UTB1 for Field
Wiring Connections

OITS PC

Comp #1 I/O

OMM 1008-1 9

Use with On-Site Generators

Magnitude chillers have their total tonnage divided between two compressors (all but single compressor Model
WMC 145S) that start sequentially and they are operated with variable frequency drives. These features make
Magnitude chillers especially appropriate for use in applications where they may be required to run with on-site
electrical generators. This is particularly true when the generators are used for temporary power when the utility
power is lost.

Starting/Stopping Procedure: The stopping of the chiller in the event of a power failure is typically uneventful.
The chiller will sense a loss of voltage and the compressors will stop, coasting down using power generated
from their dynamic braking to maintain the bearing magnetic field. The stop signal will initiate a three-minute
stop-to-start timer, effectively preventing compressor restart for three minutes. The timer is adjustable from
three to fifteen minutes, but the recommended and default value is three minutes. This interval allows the
generator sufficient time to get up to speed and stabilize. The chiller will restart automatically when the start-to­start timer expires.

Transfer Back to Grid Power: Proper transfer from stand-by generator power back to grid power is essential to
avoid compressor damage.

!

WARNING

Stop the chiller before transferring supply power from the generator back to the utility power grid.

Transferring power while the chiller is running can cause severe compressor damage.

The necessary procedure for reconnecting power from the generator back to the utility grid is show below.
These procedures are not peculiar to McQuay units only, but should be observed for any chiller manufacturer.

1. Set the generator to always run five minutes longer than the unit start-to-start timer, which could be set

from 15 to 60 minutes. The actual setting can be viewed on the operator interface panel on the
Setpoint/Timer screen.

2. Configure the transfer switch, provided with the generator, to automatically shut down the chiller before

transfer is made. The automatic shut-off function can be accomplished through a BAS interface or with
the “remote on/off” wiring connection shown in
after the stop signal since the three-minute start-to-start timer will be in effect.

Chiller Control Power: For proper operation on standby power, the chiller control power must remain as
factory-wired from a unit-mounted transformer. Do not supply chiller control power from an external power
source because the chiller may not sense a loss of power and do a normal shutdown sequence.

Figure 8

on page 29. A start signal can be given anytime

Multi-Chiller Setup

Component Description
Communication Setup

The communication wiring and setup required for dual compressor operation is performed in the
factory and should be reviewed when the chiller is initially started after installation or if there is any
change made in the chiller control hardware.
RS485 communication wiring between chillers should be field wired before start-up and installed as
a NEC Class 1 wiring system.

10 OMM 1008-1

Table 1, pLAN address and DIP Switch Settings for Controllers Using pLAN.

Chiller

(1)

A

B

Comp 1

Controller
Dec. 1 2 5 6 7 8
Bin. 100000 010000 101000 011000 N/A 000100
Dec. 9 10 13 14 15 16
Bin. 100100 010100 101100 011100 N/A 000010

Comp 2

Controller

Unit

Controller

Reserved Operator

Interface (2)

NOTES for pLAN multi-chiller communication setup:

1. Two Magnitude units can be interconnected.

2. Operator Interface Touch Screen (OITS) setting is not a DIP switch setting. The OITS address is selected by

selecting the ‘service’ set screen. Then, with the Technician level password active, select the ‘pLAN Comm’
button. Buttons A(7), B(15), C(23), D(31) will appear in the middle of the screen, then select the letters for
the OITS address for the chiller that it is on. Then close the screen. Note that A is the default setting from
the factory.

3. For the pCo2 controller, the pLAN address can be confirmed by viewing the DIP switch positions and

comparing to the table above (Bin. rows). There are six Binary DIP Switches: Up is ‘On’, indicated by ‘1’.
Down is ‘Off’, indicated by ‘0’. They are slide and not rocker switches.

Reserved

4. For the pCo3 controller, there are no DIP switches as shown below.

The pLAN address can only be confirmed as follows:

A) Disconnect pLAN (connectors J10 and J11) from all pCo2 and pCo3 controller(s).
B) Cycle power to the controller and then hold down both the Left Arrow (alarm) and the Up Arrow keys simultaneously

as the controller completes its Self-Test routine. The controller will then show you the present pLAN address of
the controller. Verify that the pLAN address matches the desired address from the above table (Dec. rows). If the
address needs to be changed, follow the instructions displayed on the pCo3 controller’s LCD display. Press enter
when done.

C) Only after all controllers pLAN addresses have been set/confirmed can the pLAN network connectors be re-

connected.

OMM 1008-1 11

Operator Interface Touch Screen (OITS) Settings

Settings for any type of linked multiple compressor operation must be made to the MicroTech II controller.
Settings on a dual compressor unit are made in the factory prior to shipment, but must be verified in the field
before startup. Settings for multiple chiller installations are set in the field on the Operator Interface Touch
Screen as follows:

Maximum Compressors ON – SETPOINTS - MODES screen, Selection #10 = 2 for a WMC, 4 for 2 WMCs.

Sequence and Staging – SETPOINTS - MODES screen, Selection #11 & #13; #12 & #14. Sequence sets the
sequence in which compressors will start. Setting all to “1” evokes the automatic lead/lag feature and is the
preferred setting.

Nominal Capacity – SETPOINTS - MOTOR screen, Selection #10. The setting is the compressor design
tons. Compressors on dual units are always of equal capacity.

Communication Setup

1. With no communication connections between chillers, disconnect control power and set the pLan

address as shown in Table 1.

2. With all manual switches off, turn on control power to each chiller and set each OITS address (see

Note 2 above).

3. Verify correct nodes on each OITS Service Screen.

4. Connect chillers together (pLAN, RS485, between J6 connections on each unit’s isolation boards.

The boards are not furnished, separate RS485 isolators must be field supplied.

5. Verify correct nodes on each OITS Service Screen. See Figure 26 on page 50.

Operating Limits:

Maximum standby ambient temperature, 130°F (55°C)

Minimum operating ambient temperature (standard), 35°F (2°C)

Leaving chilled water temperature, 36°F to 60°F (2.2°C to 15°C)

Maximum operating evaporator inlet fluid temperature, 66°F (19°C)

Maximum startup evaporator inlet fluid temperature, 90°F (32°C)

Maximum non-operating inlet fluid temperature, 100°F (38°C)

Minimum condenser water entering temperature, 55°F (12.8°C)

Maximum condenser entering temperature, 105F (40.6C)

Maximum condenser leaving temperature, 115F (46.1C)

12 OMM 1008-1

Low Condenser Water Temperature Operation

When the ambient wet bulb temperature is lower than design, the entering condenser water temperature can
be allowed to fall to improve chiller performance. This is especially true of an advanced design such as the
McQuay Magnitude chiller that features variable compressor speed.

It is an engineering fact that as the compressor discharge pressure is reduced, the amount of power to pump
a given amount of gas also is reduced. The reduction can result in significant energy savings.

However, as with most centrifugal chiller applications, a tower bypass valve must be installed and must be
controlled by the chiller MicroTech II controller. Figure 3 illustrates two temperature actuated tower
bypass arrangements. The “Cold Weather” scheme provides better startup under cold ambient air
temperature conditions. The check valve may be required to prevent entraining air at the pump inlet.

Figure 3, Bypass, Mild Weather Operation

Bypass, Cold Weather Operation

OMM 1008-1 13

Operating the Control System

Interface Panel On/Off

The Operator Interface Panel is turned on and off with a switch located at the lower front of the panel.
Screen control buttons are located to either side of it and elicit on-screen prompts when pressed.

The screen is equipped with a screen saver that blackens the screen. Touching the screen anywhere
reactivates the screen. If the screen is black, touch it first to be sure it is on before using the ON/OFF botton.

Start/Stop Unit

There are four ways to start or stop the chiller. Three are shown below and selected in SETPOINT\
MODE\SP3; the fourth way is through panel-mounted switches:

1. Operator Interface Panel (LOCAL)

Home Screen 1 has AUTO and STOP buttons that are only active when the unit is in "LOCAL
CONTROL." This prevents the unit from being accidentally started or stopped when it is normally under
control from a remote switch or BAS. When these buttons are pressed, the unit will cycle through its
normal starting or stopping sequence.

2. Remote SWITCH

Selecting SWITCH in SP3 will put the unit under the control of a remote switch that must be wired into
the control panel (see

Figure 8

on page 8).

3. BAS

BAS input is field-wired into a module that is factory-installed on the unit controller.

Control Panel Switches

The unit control panel, located adjacent to the Interface Panel, has switches inside the panel for stopping the
entire unit or individual compressors. When the UNIT switch is placed in the OFF position, the chiller will
shut down through the normal shutdown sequence whether one or two compressors are on.

The COMPRESSOR switches will immediately shut down the compressor without going through the
shutdown sequence when placed in the OFF position. It is equivalent to an emergency stop switch.

Change Setpoints

Setpoints are easily changed on the Operator Interface Touch Screen (OITS). A complete description of the
procedure begins on page 38. Setpoints can also be changed in the unit controller, but this is not
recommended except in an emergency when the OITS is unavailable.

Alarms

A red ALARM light in the lower middle of any OITS screen is illuminated if there is an alarm. If the optional
remote alarm is wired in, it too will be energized.

There are three types of alarms:

• Fault, equipment protection alarms that shut a unit or compressor off.

• Problem, limit alarms that limit compressor loading in response to an out-of-normal condition. If the

condition that caused a limit alarm is corrected, the alarm light will be cleared automatically.

• Warning, notification only, no action taken by controller.

Any type will light the ALARM light. Procedures for dealing with alarms are shown below:

1. Press the alarm light button. This will go directly to the ACTIVE ALARMS screen.

2. The alarm description (with date stamp) will be shown.

14 OMM 1008-1

3. Press the ACKNOWLEDGE button to recognize the alarm.

4. Correct the condition causing the alarm.

5. Press the CLEAR button to clear the alarm from the controller. If the fault condition is not fixed, the

alarm will continue to be on and the unit will not be able to be restarted.

Component Failure

Chiller Operation without the Operator Interface Panel

The Operator Interface Touch Screen communicates with the unit controller, displaying data and transmitting
touch screen inputs to the controllers. It does no actual controlling and the chiller can operate without it.
Should the Touch Screen become inoperable, no commands are necessary for continuing unit operation. All
normal inputs and outputs will remain functional. The unit controller can be used to view operational data, to
clear alarms and to change setpoints, if necessary.

Component Description

Operator Interface Touch Screen

The operator interface touch screen (OITS) is the primary
device for entering commands and entries into the control
system. (Settings can also be made directly into the unit
controller.) The OITS can also display controller data and
information on a series of graphic screens. A single OITS is
used per unit.

Selected information from the OITS panel can be down­loaded via a USB port located in the unit control panel.

The OITS panel is mounted on a moveable arm to allow
placement in a convenient position for the operator.

There is a screen-saver programed into the system. The
screen is reactivated by touching it anywhere.

Controller Description

Hardware Structure

The controller is fitted with a microprocessor for running the control program. There are terminals for
connection to the controlled devices (for example: solenoid valves, tower fans, pumps). The program and
settings are saved permanently in FLASH memory, preventing data loss in the event of power failure without
requiring a back-up battery.

The controller connects to other control boards, the on-board compressor microprocessors and the OITS via a
local communications network. The controller can also have an optional module to provide communication
for a BAS using standard open protocols.

OMM 1008-1 15

ALARM

Keypad

A 4-line by 20-character/line liquid crystal display and 6-button keypad is mounted on the controller. Its
layout is shown below.

Figure 4, Controller Keypad

Key-to-Screen Pathway

Air Conditioning

<

VIEW

<

SET

<

MENU Key

ARROW Keys (4)

ENTER Key with

Green Run Light

Behind

The four arrow keys (UP, DOWN, LEFT, RIGHT) have three modes of use:

• Scroll between data screens in the direction indicated by the arrows (default mode).

• Select a specific data screen in the menu matrix using dynamic labels on the right side of the display such

as ALARM, VIEW, etc (this mode is entered by pressing the MENU key). For ease of use, a pathway
connects the appropriate button to its respective label on the screen.

•

Change field values in setpoint programming mode according to the following table:
LEFT key = Default RIGHT key = Cancel
UP key = Increase (+) DOWN key = Decrease (-)
These four programming functions are indicated by one-character abbreviation on the right side of the
display. This programming mode is entered by pressing the ENTER key.

Getting Started

There are two basic procedures to learn in order to utilize the MicroTech II controller:

1. Navigating through the menu matrix to reach a desired menu screen, and knowing where a particular

screen is located.

2. Knowing what is contained in a menu screen and how to read that information, or how to change a

setpoint contained in the menu screen.

Navigating

The menus are arranged in a matrix of screens across a top horizontal row. Some of these top-level screens
have sub-screens located under them.

There are two ways to navigate through the menu matrix to reach a desired menu screen.

1) One is to scroll through the matrix from one screen to another using the four ARROW keys.

2) Another way is to use shortcuts to work through the matrix hierarchy. From any menu screen,

a) Pressing the MENU key will take you to the top level of the hierarchy. The display will show

ALARM, VIEW, and SET as shown in Figure 4. One of these choices can then be selected by
pressing the key connected to it via the pathway shown in the figure.

b) Depending on the top-level selected, a second level of screens will appear. For example, selecting

ALARM will go the next level of menus under ALARM (ALARM LOG or ACTIVE ALARM).
Selecting VIEW will go the next level of menus (VIEW COMPRESSOR STATUS, VIEW UNIT
STATUS, VIEW EVAPORATOR, or VIEW CONDENSER). Selecting SET will go to a series of
menus for looking at and changing setpoints.

16 OMM 1008-1

ALA RM LO G

show:

c) After selecting this second level, the desired screen can be acquired using the arrow keys. A typical

final screen is shown below.

Pressing the MENU key from any menu screen will automatically return you to the MENU mode.

Figure 5, Typical Menu Display and Keypad Layout

MENU Key

Air Conditioning

VIEW UNIT STATUS
Unit = COOL
Compr. #1/#2=OFF/OFF
Evap Pump = RUN

ARROW Keys

ENTER Key

Menu Screens

A hierarchical menu structure is used to access the various screens. Each menu screen can have one to four
lines of information. Optionally, the last menu selection can access one of a set of screens that can be
navigated with the UP/DOWN arrow keys (see the scrolled menu structure below). Menu selection is
initiated by pressing the MENU key, which changes the display from a data screen to a menu screen. Menu
selections are then made using the arrow keys according to labels on the right side of the display (the arrows
are ignored). When the last menu item is selected, the display changes to the selected data screen. An
example follows showing the selection of the “VIEW COMPRESSOR (n) screen. Suppose the initial screen
is:

( da ta)
( da ta)

After pressing the MENU button, the top-level menu screen will
show:

( da ta)

< ALARM
< VIEW

After pressing the “VIEW” menu button, a menu screen will

< SET
<

VIEW < COMPRESSOR
< UNIT
< EVAPORATOR
< CONDENSER

VIEW COMP (n)
(screen n data)
(screen n data)
(screen n data)

.

OMM 1008-1 17

After pressing the “COMPRESSOR” menu button, the selected
data screen will show;

Where “n” is the number of the last viewed COMPRESSOR
screen. The arrow keys will automatically return to the
“scroll” mode at this time. Different compressor screens can
then be selected with the UP/DOWN arrow keys.

Unit Controller

Table 2, Unit Controller, Analog Inputs

# Description Signal Source Range

1 Reset of Leaving Water Temperature 4-20 mA Current 0-(10 to 80°F)

Entering Evaporator Water

2

Temperature
Entering Condenser Water

3

Temperature
4 Leaving Condenser Water Temperature NTC Thermistor (10k@25°C) -58 to 212°F
5 Liquid Line Refrigerant Temperature NTC Thermistor (10k@25°C) -58 to 212°F
6 Demand Limit 4-20 mA Current 0-100 %RLA
7 Evaporator Water Flow 4 to 20 mA Current 0 to 10,000 gpm
8 Condenser Water Flow 4 to 20 mA Current 0 to 10,000 gpm
9 Refrigerant Leak Sensor 4 to 20 mA Current 0 to 100 ppm

10 Leaving Evaporator Water Temperature NTC Thermistor (10k@25°C) -58 to 212°F

Table 3, Unit Controller, Digital Inputs

# Description Signal Signal

1 Unit OFF Switch 0 VAC (Stop) 24 VAC (Auto)
2 Remote Start/Stop 0 VAC (Stop) 24 VAC (Start)
3 Not Used
4 Evaporator Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
5 Condenser Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
6 Manual Off 0 VAC (Off) 24 VAC (Auto)
7 Evaporator Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
8 Condenser Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)

NTC Thermistor (10k@25°C) -58 to 212°F

NTC Thermistor (10k@25°C) -58 to 212°F

Table 4, Unit Controller, Digital Outputs

# Description Load Output OFF Output ON

1 Evaporator Water Pump #1 Pump Contactor Pump OFF Pump ON
2 Evaporator Water Pump #2 Pump Contactor Pump OFF Pump ON
3 Condenser Water Pump #1 Pump Contactor Pump OFF Pump ON
4 Condenser Water Pump #2 Pump Contactor Pump OFF Pump ON
5 Tower Fan #1 Fan Contactor Fan OFF Fan ON
6 Tower Fan #2 Fan Contactor Fan OFF Fan ON
7 Spare
8 Alarm Alarm Indicator Alarm OFF Alarm ON
9 Tower Fan #3 Fan Contactor Fan OFF Fan ON

10 Tower Fan #4 Fan Contactor Fan OFF Fan ON

11 Compressor Off Emer. Solenoid

Circuit Breaker

ON

Circuit Breaker

OFF

Table 5, Unit Controller, Analog Outputs

# Description Output Signal Range

1 Cooling Tower Bypass Valve Position 0 to 10 VDC 0 to 100% Open
2 Cooling Tower VFD Speed 0 to 10 VDC 0 to 100%
3 EXV signal to IB Valve Control Bd. 0 to 10 VDC 0 to 100%
4 Y3 Electronic Expansion Valve 0 to 10 VDC 0 to 100% Open

Unit Controller Setpoints

The following parameters are remembered during power off, are factory set to the Default value, and can be
adjusted to any value in the Range column.

The “Type” column defines whether the setpoint is part of a coordinated set of duplicate setpoints in different
controllers. There are three possibilities as given below:

N = Normal setpoint - Not copied from, or copied to, any other controller.

M = Master setpoint - Setpoint is copied to all controllers in the “Sent To” column.

S = Slave setpoint - Setpoint is a copy of the master setpoint (in the unit controller).

18 OMM 1008-1

At power-up the slave node checks if the master node is operational and if so, it sets its copy of the setpoint
equal to the master’s. Otherwise, the setpoint remains unchanged. During normal operation, any time the
master setpoint changes, the slave is updated as well.

The PW (password) column indicates the password that must be active in order to change the setpoint. Codes
are as follows:

O = Operator, M = Manager, T = Technician (not available through the 4x20 display/keypad).

The following table groups setpoints that relate to the entire unit operation and are stored in the unit
controller. All settings are made through the OITS

Table 6, Controller Setpoints

Description Default Range Type PW

Unit

Unit Enable OFF OFF, ON M O

Control Source KEYPAD

Display Units
Language ENGLISH ENGLISH, (TBD) N O

BAS Protocol NONE

Motor Amps

Demand Limit OFF OFF, ON N O
Minimum Amps 40% 20 to 80% N T
Maximum Amps 100% 40 to 100% N T
Soft Load OFF OFF, ON D M
Begin Amp Limit 40% 20 to 100% N M
Soft Load Ramp 5 min 1 to 60 min D M
Maximum Rate
Minimum Rate

Staging

Mode Normal Normal, Efficiency, Pump, Standby N M
Sequence # 1 1,2, … (# of Compressors) N M
Maximum Compressors ON 16 1-16 G M
Stage Delta T 1.0 0.5-5.0 G M
Full Load 120 sec 30 to 300 sec N T
Absolute Capacity 100 Tons 0 to 9999 Tons D T

Leaving Water

Cool LWT
Startup Delta T
Shutdown Delta T
LWT Reset Type NONE NONE, RETURN, 4-20mA N M
Max Reset Delta T
Start Reset Delta T

Timers

Evap Recirculate 30 sec 15 sec to 5 min N M
Start-Start 40 min 15 to 60 min N M
Stop-Start 3 min 3 to 20 min N M
Source No Start

Pumps

Evap Pump

Cond Pump

Cooling Tower

Tower Control None None, Temperature, Lift N M
Tower Stages 2 1 to 4 N M

°F/psi °F/psi, °C/kPa

0.5 °F/min 0.1 to 5.0 °F/min

0.1 °F/min 0.0 to 5.0 °F/min

44. 0°F 36.0 to 60.0 °F

3.0°F 0.0 to 10.0 °F

3.0°F 0.0 to 3.0 °F

0.0°F 0.0 to 20.0 °F

10. 0°F 0.0 to 20.0 °F

70 °F 50 to 100 °F

Pump #1

Only

Pump #1

Only

Pump #1 Only, Pump #2 Only, Auto

Pump #1 Only, Pump #2 Only, Auto

Continued on next page

KEYPAD, BAS,
DIGITAL INPUT

NONE, BACnet, LonWorks,

MODBUS, N2

Lead, #1 Primary, #2 Primary

Lead, #1 Primary, #2 Primary

N O

N O

N M

D M
D M

M O
M O
M O

N M
N M

D T

N M

N M

OMM 1008-1 19

Description Default Range Type PW

Stage Up Time 2 min 1 to 60 min N M
Stage Down Time 5 min 1 to 60 min N M
Stage Differential (Temp)
Stage Differential (Lift) 6.0 psi 1.0 to 20.0 psi N M
Stage #1 On (Temp)
Stage #2 On (Temp)
Stage #3 On (Temp)
Stage #4 On (Temp)
Stage #1 On (Lift) 35 psi 10 to 130 psi N M
Stage #2 On (Lift) 45 psi 10 to 130 psi N M
Stage #3 On (Lift) 55 psi 10 to 130 psi N M
Stage #4 On (Lift) 65 psi 10 to 130 psi N M

Cooling Tower Valve / VFD

Valve/VFD Control None

Valve Setpoint (Temp)
Valve Setpoint (Lift) 30 psi 10 to 130 psi N M
Valve Deadband (Temp)
Valve Deadband (Lift) 4.0 psi 1.0 to 20.0 psi N M

Stage Down @ 20% 0 to 100% N M
Stage Up @ 80% 0 to 100% N M
Valve Control Range (Min) 10% 0 to 100% N M
Valve Control Range(Max) 90% 0 to 100% N M

Valve Type

Minimum Start Position 0% 0 to 100% N M
Minimum Position @
Maximum Start Position 100% 0 to 100% N M
Maximum Position @
Error Gain 25 10 to 99 N M
Slope Gain 25 10 to 99 N M
Alarms
Evaporator Freeze
Condenser Freeze
Low Evap Pressure 26 psi 10 to 45 psi D T
Low Evap Pressure-Inhibit 38 psi 20 to 45 psi D T
Low Evap Pressure-Unload 31 psi 20 to 45 psi D T
High Discharge Temperature-

Shutdown
High Discharge Temperature­Load
High Condenser Pressure 140 psi 120 to 240 psi D T

Motor Current Threshold 10% 1 to 20% N T
Surge High Suction SH - Start
Surge High Suction SH - Run

Service

Vane Mode AUTO AUTO, MANUAL N T
Unload Timer 10 sec 10 to 240 sec N T
STOP Timer 1 sec 1 to 240 sec N T

3.0 °F 1.0 to 10.0 °F

70 °F 40 to 120 °F
75 °F 40 to 120 °F
80 °F 40 to 120 °F
85 °F 40 to 120 °F

None, Valve Setpoint, Valve Stage,

VFD Stage, Valve SP/VFD Stage

65 °F 40 to 120 °F

2.0 °F 1.0 to 10.0 °F

NC

(To Tower)

60 °F 0 to 100 °F

90 °F 0 to 100 °F

34.0 °F -9.0 to 45.0 °F

34.0 °F -9.0 to 45.0 °F

190 °F 120 to 240 °F

170 °F 120 to 240 °F

50 °F 25 to 90 °F
25 °F 5 to 45 °F

NC, NO N M

N M

N M
N M
N M
N M

N M

N M

N M

N M

N M

D T
D T

N T

N T

N T
N T

These setpoints are normally viewed or changed on the OITS.

20 OMM 1008-1

Faults, Problems, Warnings

Faults (Equipment Protection Shutdowns)

There are no Unit protection shutdown alarms; all such alarms are handled through the compressor
controllers.

Problems (Limit Alarms)

The following alarms limit operation of the chiller in some way as described in the Action Taken column.

Table 7, Controller Limit Alarms

Description Occurs When: Action Taken Reset

Evaporator Pump #1
Fault

Evaporator Pump #2
Fault

Condenser Pump #1
Fault

Condenser Pump #2
Fault

Entering Evaporator
Water Temperature
Sensor Fault

No flow indicated for (5 sec) with Evaporator Pump #1 ON

AND [the other pump is available (per the Evap Pump

SP) AND has not faulted]

No flow indicated for (5 sec) with Evaporator Pump #2 ON

AND [the other pump is available (per the Evap Pump

SP) AND has not faulted]

No flow indicated for (5 sec) with Condenser Pump #1 ON

AND [the other pump is available (per the Evap Pump

SP) AND has not faulted]

No flow indicated for (5 sec) with Condenser Pump #2 ON

AND [the other pump is available (per the Evap Pump

SP) AND has not faulted]

Sensor fault AND leaving water reset is based on entering

water

Start pump #2 Manual

Start pump #1 Manual

Start pump #2 Manual

Start pump #1 Manual

Manual.

Reset mode is

set to No Reset

(Reset mode
goes back to

Entering

Water)

Warnings

The following “alarms” only generate a warning message to the operator. Chiller operation is not affected.

Table 8, Controller Warnings

Description Occurs When: Action Taken Reset

Entering Evaporator Temperature
Sensor Fault
Entering Condenser Temperature
Sensor Fault
Leaving Condenser Temperature
Sensor Fault
Liquid Line Refrigerant
Temperature Sensor Fault

Sensor is open or shorted Annunciation Automatic

Sensor is open or shorted Annunciation Automatic

Sensor is open or shorted Annunciation Automatic

Sensor is open or shorted Annunciation Automatic

Controller Functions

Leaving Water Temperature (LWT) Reset

The Active Leaving Water variable shall be set to the current Leaving Water Temperature (LWT) setpoint
unless modified by one of the reset methods below. (The current LWT setpoint is Cool LWT as determined
by the chiller mode.) The type of reset in effect is determined by the LWT Reset Type setpoint.

Reset Type – NONE

The Active Leaving Water variable is set equal to the current LWT setpoint.

Reset Type – RETURN

The Active Leaving Water variable is adjusted by the return water temperature.

When the chiller mode = COOL, the Active Leaving Water variable is reset using the following parameters:

OMM 1008-1 21

1. Cool LWT setpoint

2. Max Reset Delta T setpoint

3. Start Reset Delta T setpoint

Reset is accomplished by changing the Active Leaving Water variable from the (Cool LWT setpoint) to the
(Cool LWT setpoint + Max Reset Delta T setpoint) when the evaporator (return – leaving) water temperature
delta varies from the (Start Reset Delta T setpoint) to 0.

The Active Leaving Water variable is set equal to the Cool LWT setpoint if the reset signal is less than or
equal to 4 mA. It is set equal to (Cool LWT setpoint + Max Reset Delta T setpoint) if the reset signal equals
or exceeds 20 mA. The Active Leaving Water variable will vary linearly between these extremes if the reset
signal is between 4 mA and 20 mA. An example of this action is shown below.

LWT Reset (Cool mode)

(54.0°F)

(temperatures are examples only)

Max Reset Delta T

(10.0°F)

Cool LWT Set-Point

(44.0°F)

0 ma

4 ma

20 ma

22 OMM 1008-1

Compressor Controller

The compressor controller's primary function is controlling and protecting the compressor. No setpoints are
input to it. There is one compressor controller for each compressor on the unit. The compressor controller
receives, processes, and sends data to the unit controller, the compressor on-board microprocessors and to
external devices. With some operator intervention the compressor controller can operate the compressor if the
operator interface touch screen is unavailable. Inputs and outputs are as follows:

Table 9, Compressor Controller, Analog Inputs

# Description Signal Source Range

1
2 Spare
3 Motor Current 0 to 5 VDC 0 to 125% RLA

Table 10, Compressor Controller, Digital Inputs

# Description Signal Signal

1
2 Spare
3 Spare
4 Spare
5 Spare
6 Spare
7 Evaporator Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
8 Condenser Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
9 Spare

Table 11, Compressor Controller, Analog Outputs

# Description Output Signal Range

1 Spare

Table 12, Compressor Controller, Digital Outputs

# Description Load Output OFF Output ON

1
2 Spare
3 Spare
4 Spare
5 Spare
6 Spare
7 Spare
8 Inter Lock Solenoid Comp Disabled OFF Comp. Enabled ON
9 Spare

OMM 1008-1 23

Compressor Faults, Problems, Warnings

Faults (Equipment Protection Shutdowns)

Equipment protection faults cause rapid compressor shutdown. The compressor is stopped immediately (if
the compressor was running).

The following table identifies each alarm, gives the condition that causes the alarm to occur, and states the
action taken because of the alarm. All equipment protection alarms require a manual reset.

These faults are accessed by first selecting Comp 1 or Comp 2 on the controller screen

Table 13, Compressor Faults (Equipment Protection Shutdowns)

Description Occurs When: Action Taken

Low Evaporator Pressure Evaporator Press < Low Evap Pressure SP Rapid Stop

High Condenser Pressure Cond Press > High Condenser Pressure SP Rapid Stop

Low Motor Current I < Motor Current Threshold with Compressor ON for 30 sec Rapid Stop

High Discharge Temperature Temp > High Discharge Temperature SP Rapid Stop

Mechanical High Pressure Digital Input = High Pressure Rapid Stop

High Motor Temperature Digital Input = High Temperature Rapid Stop

Surge High Suct SH-Starting

Surge High Suct SH-Running

No Compressor Stop

Starter Fault

Leaving Evaporator Water
Temperature Sensor Fault

Evaporator Pressure Sensor Fault Sensor shorted or open Rapid Stop

Condenser Pressure Sensor Fault Sensor shorted or open Rapid Stop

Suction Temperature Sensor Fault Sensor shorted or open Rapid Stop
Discharge Temperature Sensor

Fault
Evaporator Water Flow Loss Evaporator Flow DI = No Flow for > 10 sec Rapid Stop

Condenser Water Flow Loss Condenser Flow DI = No Flow for > 10 sec Rapid Stop

Temp > Surge High Suct SH-Start SP during first 5 minutes

of Compressor ON

Temp > Surge High Suct SH-Run SP after first 5 minutes of

Compressor ON

%RLA > Motor Current Threshold SP with Compressor OFF

for 30 sec

Starter Fault Digital Input = Fault AND Compressor State =

START, INTLOK, RUN, or UNLOAD

Sensor shorted or open Rapid Stop

Sensor shorted or open Rapid Stop

Rapid Stop

Rapid Stop

Annunciation

Rapid Stop

Compressor Events (Limit Alarms)

The following alarms do not cause compressor shutdown but limit operation of the chiller as described in the
Action Taken column.

Table 14, Compressor Events

Description Occurs When: Action Taken Automatic Reset

Low Evaporator Pressure
– Inhibit Loading
Low Evaporator Pressure
– Unload
Evaporator Freeze
Protect
Condenser Freeze
Protect

High Discharge
Temperature

24 OMM 1008-1

Pressure < Low Evap Pressure–Inhibit

Pressure < Low Evap Pressure–Unload

Evap Sat Refr Temp < Evaporator Freeze

Cond Sat Refr Temp < Condenser Freeze

Temperature > High Discharge

Temperature-Load SP AND

Suction superheat < 15°F

setpoint

setpoint

setpoint

Setpoint

Inhibit loading

Unload

Start evaporator

pump

Start condenser

pump

Load

Evap Press rises above

(SP + 3psi)

Evap Press rises above

(SP + 3psi)

Temp > (Evaporator Freeze

SP + 2°F)

Temp > (Condenser Freeze

SP + 2°F)

Temp < (High Dsch Temp

Load SP – 3°F) OR

Superheat > 18°F

Warnings

Warnings advise that a non-catastrophic problem exists, such as failed temperature sensor that provides a
signal for information, not control purposes. There are no Warnings associated with the compressor
controllers.

Compressor Control Functions

Each compressor determines if it has reached its maximum capacity (or maximum allowed capacity) and if
so, set its Full Load flag. The flag is based on a number of conditions.

Absolute Capacity

Each compressor estimates its absolute capacity from the present value of % RLA and the Absolute Capacity
setpoint from the equation:

Absolute Capacity = (%RLA Factor) * (Absolute Capacity setpoint)
where the %RLA Factor is interpolated from the following table.

%RLA 0 50 75 100 150
%RLA Factor 0 0.35 0.75 1.00 1.50

Multiple Compressor Staging

This section defines which compressor is the next one to start or stop. The next section defines when the
start, or stop, is to occur.

Functions

1. Can start/stop compressors according to an operator defined sequence.

2. Can start compressors based on the number of starts (run hours if starts are equal) and stop on run hours.

3. The above two modes can be combined so that there are two or more groups where all compressors in the

first group are started (based on number of starts/hours) before any in the second group, etc. Conversely,
all compressors in a group are stopped (based on run hours) before any in the preceding group, etc.

4. An “efficiency priority” mode can be selected for two or more chillers where one compressor is started

on each chiller in the group before a second is started on any of them.

5. A “pump priority” mode can be selected for one or more chillers where all compressors on a given chiller

are started before going to the next chiller in the group.

6. One or more compressor can be defined as “standby” where it is never used unless one of the normal

compressors is unavailable.

Required Parameters

1. Sequence number setpoint (SQ#_SP) for all compressors. Possible settings = (1-4).

2.

Compressor Staging Mode setpoint (CSM_SP) for all compressors. Possible settings are:

NORMAL

••

EFFICIENCY PRIORITY

••

PUMP PRIORITY

••

STANDBY

••

3. Maximum Number of compressors ON setpoint (MAX_ON_SP). Possible settings = (1-4). This setpoint

is the same for all compressors.

4. Number of starts for all compressors.

5. Number of run hours for all compressors.

6. Status of all compressors (On-line, Available/Unavailable, Starting, Running, etc.)

OMM 1008-1 25

I

nterLok Timer Expired

Unload Timer Expired

Safety Alarm

&

STOP Timer Expired

Configuration Rules

1. Each standby compressor must have a sequence number greater than or equal to all non-standby

compressors for which it is in standby.

2. All compressors in an “efficiency priority” or “pump priority” group must be set to the same sequence

number.

Compressor State Control (Comp State)

Operation of the compressor is controlled by the state-transition diagram shown below. A state variable
(Comp State) shall be used to maintain the current state (OFF, START, INTLOK, RUN, UNLOAD, or STOP).
Transitions from one state to another are controlled by the condition statements in the TEST boxes. TASK
boxes indicate actions that must be performed.

Figure 6,Compressor State

Power ON

TEST: Motor Current < Motor Current Threshold SP

OFF

TEST:

Unit State=AUTO & Evap State=RUN & Next On = Yes &

Stage Up Now = YES & (Unit Mode NOT= HEAT OR

EvLWT Temperature > Source No Start SP) &

Start-Start Timer Expired & Stop-Start Timer Expired &

No Safety Alarms

TASK: Restart Start-Start Timer

VaneCloseDelay

TEST: Manual OFF DI = OFF OR

Vanes Closed OR Unit State = OFF

OR

TASK: Start STOP Timer

Start Stop-Start Timer & Update Run Hours

OR

UNLOAD

TEST: Manual OFF DI = OFF

OR Unit State = OFF

TEST: Unit State = AUTO

& Next Off = No

TEST: Manual OFF DI = OFF OR

Unit State = (OFF OR SHUTDOWN)

OR Safety Alarm

START

TASK: Start Interlok Timer (10sec)

InterLock

TEST: Unit State = SHUTDOWN OR

[Next Off = Yes & Stage Down Now = Yes]

RUN

TASK: Start Unload Timer

TEST: Unit State= AUTO & Evap State=RUN &

Cond State = RUN & Vanes Closed &

TASK: Increment # of starts

Compressor Capacity Control

Leaving Water Control Mode

Compressor capacity is determined by the status of the leaving chilled water temperature (LWT), which is a
direct indicator of whether the chiller is producing enough cooling to satisfy the cooling load. The LWT is
compared to the active chilled water setpoint, and compressor loading or unloading ensues, considering any
capacity overrides that may be in effect.

Capacity Overrides

The conditions described in the following subparagraphs override normal capacity control when the chiller is
in the COOL mode. These overrides are not in effect for loading and unloading when the Vane Mode is set to

26 OMM 1008-1