62 WGS 130A to 190A OM WGS-5
Superheat Control
In superheat control, suction superheat is controlled directly by the EXV. The superheat
target varies linearly from 6 to 10 degrees F as discharge superheat changes from 30
degrees F to 22 degrees F. PID logic controls the superheat to the target value.
When the EXV transitions to the superheat control state, the target will start at the current
suction superheat value. This target will then decrement 0.1 degree F every second until
reaching the normal target.
Closed
Any time the EXV is not in pressure control or superheat control, it will be in a closed
state. At this time, the EXV position is 0 steps and the EXV close signal (digital output) is
active.
After the compressor performs a pumpdown and cycles off, the electronic expansion valve
will re-open for 30 seconds. After these 30 seconds, the expansion valve will return to its
closed position. This logic has been added to help prevent hydraulic lock between the
liquid line solenoid and the electronic expansion valve.
EXV State Transitions
The following state diagram shows the transitions between EXV control states for both
packaged water-cooled and remote air-cooled condenser configurations. Preopen is not
performed for remote air cooled condenser configurations when the evaporator pressure is
greater than condenser pressure. See “EXV State Transitions – Aircooled” on page 63.
Power ON
Closed
Superheat
Pressure
T1
EXV States
Preopen
T5
T2
T6T7
T3
T4
Transitions:
T1 – Transition from Closed to Preopen
Requires all of the following
Unit State = Auto
Evap State = Run
Compressor is available
Compressor is next on
Stage up now flag is set
Compressor State = Off
OR (as in the case when a circuit cycles off)
Compressor State = Off and unit configured for remote air-cooled condenser,
(will perform a pre-open for 30 seconds (post open time) then return to Closed state)
T2 – Transition from Preopen to Pressure Control
Requires the following
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