7
−
12
62-11389
Alarm
NO.
Steps
Alarm/Cause
Corrective Action
18
LOW REFRIGERANT PRESSURE
•
TRIGGER–ON:
The compressor is operating with the suction pressure less than -10 in Hg (-0.3 BAR), with both the
Front (UL1) and the Rear (UL2) unloaders energized, and the time that is selected for the LP Shut-
down Delay Configuration has expired since UL1 was energized (
Note:
The MessageCenter does
not display in.Hg. This alarm triggers on when the display shows less than -4.7 psig.
•
UNIT CONTROL:
Engine Operation: alarm only or (if configured for shutdown) engine and unit
shutdown and alarm.
Standby Operation: alarm only or (if configured for shutdown) refrigeration
system shutdown and alarm with PSCON still energized.
•
RESET CONDITION: If alarm only, auto reset when either UL1 or UL2 is de-energized. If unit and
system shutdown and alarm, auto reset after 15 minutes. Alarm may be manually reset via keypad
or by turning the unit OFF, then ON again.
NOTE: Follow the steps below until a problem is found. Once a repair or correction has been made, the active
alarm should clear itself (see reset condition above). Operate the unit through the appropriate modes to see if
any active alarm occurs. Continue with the steps below as necessary.
1
Check Refrigerant Charge
Check for undercharged system.
Refer to Section 8.6.2.
2
Check System Pressures
Install manifold gauge set and check
and compare compressor discharge
& suction pressures with those
shown on the microprocessor dis-
play.
Suction pressure must be above 3 psig (0.2 bar.)
Suction & Discharge Pressures must have the same
reading on gauges & on microprocessor display.
NOTE: Microprocessor suction (CSP) and evaporator
(EVOP) pressure readings have a maximum value of
100 psig (7.5 bar) The actual suction pressure must
be lower than 100 psig in order to perform this test.
3
Manually Defrost Unit
Defrost unit and terminate automati-
cally.
Typical defrost cycle time is 5-20 minutes.
Visually verify that all ice is cleared from evaporator
coil.
4
Perform Pretrip Check
Clear Active Alarm list, then run Pre-
trip & check for any new alarms.
Any active alarms must be corrected and cleared
before proceeding.
5
Check Unloader Operation
Check Front (UL1) and Rear (UL2)
Unloaders.
Refer to Alarms 85 and 86.
6
Check CSMV
a. Check compressor suction
modulation valve.
Refer to Section 8.8.5
.
b. Check airflow (with unit running.)
Even airflow through the entire coil.
No “dead” spots.
Additional steps on the next page.
