Unit installation

36 ACZ 010A through 039A IOMM ACZ1-2
Compressor State
A compressor will start when all of the following are true:
• The compressor is “next on”
• Stage Up Now is set
• The compressor is available to start
A compressor will stop when any of the following conditions are true:
• Unit state = Off
• Evap flow alarm active
• Low Ambient start attempt failed
• Stage Down Now is set, both compressors are running, and the compressor is “next
off”
• Pumpdown is complete
Normal Shutdown
If a condition arises that requires the unit to shut down, a pumpdown will be performed if it
is not an emergency situation. A normal shutdown will be initiated when any of the
following occur:
• Unit State = Pumpdown
• Low Ambient Lockout
• A normal stagedown occurs, and only one compressor is running
Pumpdown 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 pumpdown pressure, then stop
compressor
• If evaporator pressure does not reach pumpdown pressure within two minutes, stop
compressor and log pumpdown failure alarm
Rapid Shutdown
A situation may arise that requires the unit to shut down immediately, without doing a
pumpdown. This rapid shutdown will be triggered by any of the following:
• Unit State = Off
• Stop Alarm
• Low ambient start attempt failed
All compressor and liquid line outputs will be turned off immediately for a rapid shutdown.
Liquid Line Solenoid
The liquid line output will be on any time a compressor is running and the unit is not
performing a pumpdown. This output will be off at all other times.