42 TGZ 040A through TGZ 190A OMM TGZ-1
Evaporator Water Pump State Control (Evap State)
The state-transition diagram shown below controls operation of the evaporator pump.
Off
Run Start
Unit State=Auto OR
Evap Water Freeze Alarm
Unit State = Off AND
No Evap Water Freeze Alarm
[Evap Pump State = Start
AND Flow Switch Closed]
for time > Evap Recirc Tmr
Unit State = Off AND
No Evap Water Freeze Alarm
Evaporator Pump State Diagram
Pump Selection
The pump output used will be determined by the Evap Pump Control set point. The setting
allows the following configurations:
#1 only – Pump 1 will always be used.
#2 only – Pump 2 will always be used.
Auto – The primary pump is the one with the least run hours, the other is used as a backup.
#1 Primary – Pump 1 is used normally, with pump 2 as a backup.
#2 Primary – Pump 2 is used normally, with pump 1 as a backup.
Primary/Standby Pump Staging
The pump designated as primary will start first. If the evaporator state is start for a time
greater than the recirculate timeout set point and there is no flow, then the primary pump
will shut off and the standby pump will start. When the evaporator is in the run state, if
flow is lost for more than half of the flow proof set point value, the primary pump will shut
off and the standby pump will start. Once the standby pump is started, the flow loss alarm
logic will apply if flow cannot be established in the evaporator start state, or if the flow is
lost in the evaporator run state.
Auto Control
If auto pump control is selected, the primary/standby logic above is till used. When the
evaporator is not in the run state, the run hours of the pumps will be compared. The pump
with the least hours will be designated as the primary at this time.
Evaporator Water Flow Loss
The Evaporator Water Flow Loss logic allows the Unit to shutdown compressors on a loss
of flow up to two times every twenty-four hours before locking the unit out on a Evaporator
Flow Loss Alarm.
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