52 TGZ 040A through TGZ 190A OMM TGZ-1
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.
EXV Control
The EXV control logic is active (but not necessarily used) regardless of the valve type
setting. While a circuit is in the run state, the EXV controls suction superheat. The
superheat target is 8
o
F. PID logic will be used to control the superheat to the target value.
Any time the circuit is not in the run state, the EXV position should be 0.
EXV Control Range
The table below shows the EXV range based on the number of compressors running and
number of compressors on unit.
Compressors Running
Number of
Compressors
Valve
Position
1 2 3
EXV Min 8% 8% -
4
EXV Max 60% 100% -
EXV Min 8% 8% 8%
6
EXV Max 35% 45% 65%
Manual EXV Control
The EXV position can be set manually. Manual control can only be selected when the
circuit is in the run state. At any other time, the EXV control set point is forced to auto.
When EXV control is set to auto, the manual EXV position setting follows the auto control
position. When EXV control is set to manual, the EXV position is equal to the manual
EXV position setting.
Maximum EXV Operating Pressure
This logic only applies to TGZ units equipped with electronic expansion valves (Models
TGZ 150-190). The purpose of this logic is to prevent the operating circuit’s evaporator
pressure from exceeding the ‘MaxOpPress’ set point (found on “SET COMP SPs (6)
screen) and overloading the compressors. The electronic expansion valves (EEV) will close
to prevent the operating circuit’s evaporator pressure from exceeding the ‘MaxOpPress’ set
point.
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