OMM 1087-1
AGZ 025D through 190D
41
Low Evaporator Pressure - Unload
Trigger:
This event is triggered if all of the following are true:
•
circuit state = Run
•
more than one compressor is running on the circuit
•
evaporator pressure <= Low Evaporator Pressure - Unload set point for a time greater than
half of the current freezestat time
•
circuit is not currently in a low OAT start
•
it has been at least 30 seconds since a compressor has started on the circuit.
On units equipped with 6 compressors, electronic expansion valves, and 10 or more fans, when each
compressors starts, there should be a 2 minute window during which the evaporator pressure must
drop an additional 27 KPA (3.9 PSI) to trigger the alarm. After this 2 minute window, the trigger point
should return to normal.
Action Taken:
Stage off one compressor on the circuit every 10 seconds, except the last one.
Reset:
While still running, the event will be reset if evaporator pressure > Low Evaporator Pressure
Hold SP + 90 KPA(13 PSI). The event is also reset if the circuit is no longer in the run state.
High Condenser Pressure - Unload
Trigger:
This event is triggered if all of the following are true:
•
circuit state = Run
•
more than one compressor is running on the circuit
•
condenser pressure > High Condenser Pressure – Unload set point
Action Taken:
Stage off one compressor on the circuit every 10 seconds while condenser pressure is
higher than the unload set point, except the last one. Inhibit staging more compressors on until the
condition resets.
Reset:
While still running, the event will be reset if condenser pressure <= High Condenser Pressure
Unload SP – 862 KPA(125 PSI). The event is also reset if the circuit is no longer in the run state.
Circuit Warning Alarms
Failed Pumpdown
Trigger:
Circuit state = pumpdown for longer than 2 minutes
Action Taken:
Rapid stop circuit
Reset:
N/A.
Events
Situations may arise that require some action from the chiller or that should be logged for future
reference, but aren’t severe enough to track as alarms. These events are stored in a log separate from
alarms. This log shows the time and date of the latest occurrence, the count of occurrences for the
current day, and the count of occurrences for each of the previous 7 days.
Summary of Contents for AGZ-D 25
Page 12: ...12 AGZ 025D through 190D OMM 1087 1 Figure 2 Typical Field Control Wiring...
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