Emerson Liebert iCOM Manual De Usuario

When the compressor starts, the low-pressure input is ignored for a selected period of time based on 

the setting of the Low Pressure Alarm Delay (Service Menu, Options Setup). This time is usually set 

to 3 minutes on air-cooled units, and to 0 or 1 minute on water cooled units. When this time is 

expired, a second timer starts to operate if the low-pressure input is active. This second timer is active 

during normal compressor operation to avoid compressor trips due to bubbles in the refrigerant or 

other influences creating short trips of the low-pressure switch. The low-pressure switch input is 

enabled only if the compressor is operating. Exception: Pump Down (see Pump Down).

Pump Down
The Pump Down operation is performed to protect 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 a compressor is turned Off and the low-pressure switch is closed (pressure OK), the com-

pressor will be operated with the LLSV (liquid line solenoid valve) closed (de-energized) until the low-

pressure switch opens (low-pressure condition, without giving alarm). When there is a call to turn off 

a compressor the LLSV is closed. If the low suction pressure switch (LPS) does not open within a spec-

ified time, the LLSV is turned On then back Off (to try to unstick the LLSV). The control will then 

wait a set period of time for the LPS to open. This will happen three times. If, after three times, the 

low suction pressure switch 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 LPS opens again after the compressor has been already stopped—a 

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 (LPS opened), pump down will be 

continued for another half-second with the control solenoid valve energized.

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 cor-

recting 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. Setting the counter to 0 will auto-reset 

the alarm without the need of pressing the reset button on the display. Even if the pressure in the 

system drops below the alarm point, the compressor will remain off until the system is reset.