KOMAC00607-09EN 31
• Circuit switch is closed
• No circuit alarms are active
• Circuit Mode set point is set to Enable
• BAS Circuit Mode set point is set to Auto
• No cycle timers are active
• Discharge Temperature is at least 5°C higher than Oil Saturated Temperature
Starting
The circuit will start if all these conditions are true:
• Adequate pressure in the evaporator and condenser (see No Pressure At Start Alarm)
• Circuit Switch is closed
• Circuit Mode set point is set to Enable
• BAS Circuit Mode set point is set to Auto
• No cycle timers are active
• No alarms are active
• Staging logic requires this circuit to start
• Unit state is Auto
• Evaporator pump state is Run
Circuit Startup Logic
Circuit startup is the time period following the starting of the compressor on a circuit.
During the startup, the low evaporator pressure alarm logic is ignored. When the
compressor has been running at least 20 seconds and the evaporator pressure rises above
the low evaporator pressure unload set point, the startup is complete.
If the pressure does not rise above the unload set point and the circuit has been running
longer than the Startup Time set point, then the circuit is turned off and an alarm
triggered. If the evaporator pressure drops below the absolute low pressure limit then
the circuit is turned off and the same alarm triggered.
Low OAT Restart Logic
Low OAT restart logic allows multiple start attempts in low ambient conditions. If the
condenser saturated temperature is less than 60°F when the compressor starts, the startup
is considered to be a ‘low OAT start’. If a low OAT start is not successful the circuit is
shut down, but no alarm is triggered for the first two attempts of the day. If a third low
OAT start attempt fails, then the circuit is shut down and the Low OAT Restart Alarm is
triggered.
The restart counter is reset when a startup is successful, the Low OAT Restart alarm is
triggered, or the unit time clock shows that a new day has started.
Stopping
Normal Shutdown
A normal shutdown requires the circuit to pumpdown before the compressor is turned
off. This is done by closing the EXV, and closing the liquid line solenoid (if present)
while the compressor is running.
The circuit will do a normal shutdown (pumpdown) if any of the following are true:
• Staging logic requires this circuit to stop
• Unit State is Pumpdown
• A pumpdown alarm occurs on the circuit
• Circuit switch is open
• Circuit Mode set point is set to Disable
• BAS Circuit Mode set point is set to Off
The normal shutdown is complete when any of the following are true:
• Evaporator Pressure is less than the Pumpdown Pressure set point
• Service Pumpdown set point is set to Yes and Evaporator Pressure is less than
5 psi
• Circuit has been pumping down for longer than the Pumpdown Time Limit setpoint
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