User manual

Operation
Liebert
®
iCOM
®
22
Pump Down
Pump Down is applicable to compressorized systems that are equipped for pump-down operation,
which is set at the factory. This operation prevents the compressor oil from being diluted with liquid
refrigerant to ensure that the compressor is properly lubricated for the next startup.
The Pump Down operation operates in the following manner:
Whenever the control determines that no more cooling is required and a compressor needs to be shut
Off, the liquid line solenoid valve (LLSV) is closed (de-energized). The compressor will continue to
operate until the low suction pressure device (LPS or LPT) opens, which shuts Off the compressor. If
the LP device does not open within a specified time, the LLSV is turned On, then back Off (the
assumption is that the LLSV is stuck). If, after three times, the LP device does not open, the
compressor and LLSV are locked Off and an alarm “Pump Down not completed” will appear.
There is a re-pump down if the LP device opens again after the compressor has been already
stoppered maximum of six re-pump-down cycles per hour are allowed. At the seventh request of re-
pump down, the alarm “Comp 1 Pumpdown Fail” or “Comp 2 Pumpdown Fail” will appear and the
compressor will be locked out.
Pump down is always performed loaded (for compressors with unloaders: unloaders Off, digital scroll:
control solenoid valve disabled).
For digital scroll only: when pump down has finished successfully (LP device opened), pump down will
be continued for another half-second with the control solenoid valve energized.
High Pressure Alarm
When the compressor is initially activated, the system will be monitored for a high pressure situation.
When a high pressure situation is detected during the first 10 minutes of operation, the unit will
attempt to correct the problem several times without notification. If the unit is unsuccessful in
correcting the problem, an alarm will occur and the affected compressor will be locked Off. If high
head pressure alarm trips three times in a rolling 12 hour period, the affected compressor will be
locked Off.
After the compressor has been running for 10 minutes, if a high head pressure situation is detected,
an alarm will occur and the affected compressor will be immediately locked Off without the unit
trying to correct the problem.
Once the compressor is locked Off, it will not come back On until main power is reset or until the
HP Alarm Counters (Service Menu, Diagnostics) are reset to 0.
Figure 20 Diagnostics/service mode screen, page 1 of 8
NOTE
The default setting for Pump Down is YES. The function is not available on all units. Emerson
removed pump down control from Thermal Management products in 2011. Units shipped in
2011 and before may have pump down enabled.
HP Alarm Counters