McQuay WGS130AA: WGS140AW, Operating Manual

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44 WGS 130A to 190A OM WGS-5
T3 – Transition from Pumpdown to Off
Requires any of the following

All circuits have finished pumpdown and are off

A unit alarm is active

Unit switch is “off”
T4 – Transition from Auto to Off
Requires any of the following

Unit switch is “off”

A unit alarm is active

All circuits are unavailable to start (cannot start even after any cycle timers have
expired)

The unit mode is ice, all circuits are off, and the ice mode delay is active
Ice Mode Start Delay
An adjustable start to start ice delay timer will limit the frequency with which the chiller
may start in Ice mode. The timer starts when the first compressor starts while the unit is in
ice mode. While this timer is active, the chiller cannot restart in Ice mode. The time delay
is user adjustable.
The ice delay timer may be manually cleared to force a restart in ice mode. A setpoint
specifically for clearing the ice mode delay is available. In addition, cycling the power to
the controller will clear the ice delay timer.
Evaporator Pump Control
The state-transition diagram shown below controls operation of the evaporator pump.
Power ON
OFF
RUN
START
T1
T4
T2
T3
Evaporator Pump
States
T5
Transitions:
T1 – Transition from Off to Start
Requires any of the following

Unit state = Auto AND [If Low OAT Lockout active then LWT <=40]

LWT < Freeze setpoint - 1
T2 – Transition from Start to Run

Flow ok for time > evaporator recirculate time