OMM 1087 AGZ 025D through 190D 31
Pumpdown Procedure
Pumpdown is performed as follows:
If multiple compressors are running, shut off
the appropriate compressors based on
sequencing logic and leave only one 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
Low Ambient Starts
A low OAT start is initiated if the condenser
refrigerant saturated temperature is less than
29.5°C (85.1° F) when the first compressor starts.
Once the compressor starts the circuit is in a low
OAT start state for a time equal to the Low OAT
Start Time set point. During Low OAT Starts, the
freezestat logic for the low evaporator pressure
alarm as well as the low evaporator pressure hold
and unload alarms are disabled. The absolute limit
for low evaporator pressure is enforced and the
low evaporator pressure alarm should trigger if the
evaporator pressure drops below that limit.
When the Low OAT Start Timer has expired, if
the evaporator pressure is greater than or equal to
the Low Evaporator Pressure Unload set point, the
start is considered successful and normal alarm
and event logic is reinstated. If the evaporator
pressure is less than the Low Evaporator Pressure
Unload set point when the Low OAT Start Timer
expires, the start is unsuccessful and the
compressor will shutdown.
Multiple Low Ambient Start attempts are allowed.
On the third failed Low Ambient Start attempt the
Restart Alarm is triggered and the circuit will not
attempt to restart until the Restart alarm has been
cleared.
The restart counter should be reset when either a
startup is successful, the Low OAT Restart alarm
is triggered, or the unit time clock shows that a
new day has started.
Circuit Status
The displayed circuit status should be determined by the conditions in the following table:
Enum Status Conditions
0 Off:Ready Circuit is ready to start when needed.
1 Off:Cycle Timers
Circuit is off and cannot start due to active cycle timer on all
compressors.
2 Off:All Comp Disable
Circuit is off and cannot start due to all compressors being
disabled.
3 Off:Keypad Disable Circuit is off and cannot start due to circuit enable set point.
4 Off:Circuit Switch Circuit is off and circuit switch is off.
5 Off:Alarm Circuit is off and cannot start due to active circuit alarm.
6 Off:Test Mode Circuit is in test mode.
7 Preopen Circuit is in preopen state.
8 Run:Pumpdown Circuit is in pumpdown state.
9 Run:Normal Circuit is in run state and running normally.
10 Run:Evap Press Low Circuit is running and cannot load due to low evaporator pressure.
11 Run:Cond Press High Circuit is running and cannot load due to high condenser pressure.
12 Run:High OAT Limit
Circuit is running and cannot add more compressors due to the
high ambient limit on unit capacity. Applies only to circuit 2.
Compressor Control
Compressors should run only when the circuit is in a run or pumpdown state. They should not be running
when the circuit is in any other state.
Starting a Compressor
A compressor should start if it receives a start command from the unit capacity control logic.
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