Compressor Motor Overload; Compressor Timing-Short-Cycle Protection; Compressor Sequencing On Two-Compressor Units - Emerson Liebert iCOM Manual

Supported Compressor Types
• 4-Step
• Digital Scroll
• Tandem Digital
• No standard scroll support
Digital Scroll High Temperature
A protective maximum operating compressor temperature limit is imposed on units with digital scroll
compressor(s) with thermistor. If the digital scroll temperature reaches the maximum temperature
threshold, the compressor will be locked out for at least 30 minutes and an alarm will be annunciated.
If after 30 minutes the temperature has cooled to a safe operating temperature, the compressor will
resume operation.
Each time a high-temperature alarm occurs, HT 1 Alarm Counter (Service Menu, Diagnostics) or
HT 2 Alarm Counter (Service Menu, Diagnostics) is increased by one. Once these counters reach five
occurrences in a rolling four-hour period, the compressor will be locked out. The alarm can be reset
once the temperature returns to a safe level by:
1. Setting the counter back to 0 from the display and pressing the alarm reset button.
2. Shutting off power to the control board by turning the cooling unit's main power disconnect switch
Off and On.
3.1.4

Compressor Motor Overload

When a compressor's motor overload becomes active for 10 continuous seconds, the motor overload
alarm associated with the compressor will be activated and displayed on the Liebert iCOM Screen.
While a compressor overload has been activated the compressor will be turned Off, and the lead-lag
order of the tandem banks will be reversed.
3.1.5 Compressor Timing—Short-Cycle Protection
To help maximize the life of your compressor(s), there is a start-to-next start delay for each single
compressor.
NOTE
This delay may cause a short cycle if there is a very light room load. A short cycle means that
the compressor has cycled On and Off 10 times in the past hour. This is typically caused by a
lack of load or by control settings being set too tight (see 3.4 - Temperature Control—Reheat
for more information on the control adjustment). Should short cycling still occur after the
control has been adjusted, contact technical support at 800-543-2778 to adjust the minimum
compressor Off delay.
3.1.6

Compressor Sequencing on Two-Compressor Units

Compressor Sequencing parameter (Service Menu, Options Setup) is intended to maintain equal run
times between compressors. This setting has three selection possibilities:
• Always use Compressor 1 as lead compressor.
• Always use Compressor 2 as lead compressor.
• Auto:
• First priority: If the safety timings are acceptable for only one compressor, then it is the next
to be started/stopped.
• If both compressors are Off: The one with fewer working hours is the next to start.
• If both compressors are in operation: The one that has been operating longer since the last
start is the next to be stopped.
NOTE
The Auto setting attempts to maintain equal run times between compressors. However, the
control will not turn Off a compressor to equalize run time when it is needed to control the
space. Compressor run time may become unbalanced on a Liebert DSE if the unit frequently
operates in mixed mode. Mixed mode operation is programmed to operate Compressor #2.
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Operation
® ®
Liebert iCOM for Liebert DSE
™