Pump Down; Low Pressure Switches - Emerson Liebert iCOM Training And Service Manual

iCOM
Controls Training and Service Manual

Pump Down

If the pump down parameter is enabled and when there is a call to turn off a
compressor the LLSV is closed. If the low suction transducer value does not
reach the pumpdown cutout parameter value within 60 seconds the LLSV is turned
on than back off (to try to un-stick the LLSV). The control waits another 60
seconds trying to reach the cutout value, this process will be repeated 3 times. If,
after 3 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.
An additional internal program called pumpdown recycle is used to control
compressor pump cycling. The control will re-pump down the compressor circuit
if the transducer-value goes higher than the pumpdown recycle parameter value
after the compressor has been stopped (turned off). A maximum of 6 re pump
down cycles per hour are allowed by the control per compressor circuit. At the 7
request of re-pump down the alarm "Pump Down Fail" will appear and the
compressor will be locked out.
Pump down is always performed loaded (for compressors with unloaders:
unloader off, digital scroll: control solenoid valve disabled).

Low Pressure Switches

Units supplied with low pressure switches have fixed cut-in and cut-out values.
Parameter A116 Low Pressure Device Type should be set to SWITCH.
When the compressor starts, the low-pressure digital input is ignored for a
selected period of time. This time value is set to 3 minutes (factory default) on air-
cooled units and to 0 minutes (factory default) on water and glycol cooled units.
Call for Compressor (Cooling or Dehumidification) w/Pressure Switches
After a Call for Cooling (CFC):
a) With Low Pressure Delay Time set to = 0: the LLSV opens, after one input
OK reading the compressor starts (earliest 1 second after LLSV) Flow
moves to phase 3 for both, digital scroll and all compressors.
b) With Low Pressure Delay Time set to ≠ 0: the LLSV opens, 1 second later
the compressor starts.
The "flow" is now in Phase 1.
NON DigiScroll compressors
Let the compressor continue to run for LPDT value. If at the end of the LPDT time
the switch is closed the flow moves to "Loss of Charge Protection" (Phase 3), and
Phase 1 is finished.
Note: Semi-hermetic (4-step) compressors shall run @100% (capacity valve off)
during the whole LPDT sequence.
42
th