50 WGZ030D through WGZ200D OMM 1130
triggered, the evaporator water pump will remain off and no compressors will start until the OAT rises to
the lockout set point plus 5F.
Manual Compressor Control
The operator can manually enable and disable individual compressors. When a compressor has been
disabled it is considered unavailable to start in the staging logic. With Manual Compressor control it is
possible to take a damaged compressor offline while the remaining compressors on the circuit can still
provide some cooling.
A running compressor can not be disabled until it has been shutdown. If both of the compressors on a
circuit have been disabled then the circuit is disabled. If both circuits have all of their compressors
disabled, the Unit state will remain “Off”.
Normal Circuit Shutdown
If a condition arises that requires a circuit to shut down, but it is not an emergency situation, then the
circuit will do a pump down. A normal circuit shutdown will be initiated when any of the following
occur:
Unit State = Pump Down
Circuit Switch = Off
Low Ambient Lockout
A normal stage down occurs, and only one compressor on the circuit is running
Unit mode = Ice AND the ice set point is reached
Pump Down Procedure
If both compressors are running, shut off the appropriate compressor based on sequencing logic
With one compressor left running, turn off hot gas output and liquid line output
Keep running until evaporator pressure reaches the pump down pressure, then stop compressor
If evaporator pressure does not reach pump down pressure within two minutes, stop compressor and
record a Failed Pumpdown event in the Event Log.
Rapid Circuit Shutdown
A situation may arise that requires a circuit to shut down immediately, without doing a pumpdown. This
rapid shutdown will be triggered by any of the following:
Unit State = Off
Circuit Alarm
Low ambient start attempt failed
All compressors, hot gas, and liquid line outputs should be turned off immediately for a rapid shutdown.
Liquid Line Solenoid
The liquid line output shall be on any time a compressor on the circuit is running and the circuit is not
performing a pump down. This output should be off at all other times.
Hot Gas Bypass Solenoid
This output shall be on when one compressor on the circuit is running and the circuit is not performing a
pump down. The output should be off at all other times including the delay time described below.
The hot gas bypass valve opening will be delayed for Hot Gas Bypass Time set point seconds (the default
is 30 seconds) when the first compressor starts on each circuit.
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