62-11389
7
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85
Alarm
NO.
Steps
Alarm/Cause
Corrective Action
P178 CHECK UL1
•
TRIGGER–ON: The pressure differential between suction and discharge pressures did not change
as expected when the Front Unloader (UL1) was de-energized / loaded (discharge pressure should
rise and suction pressure should drop) or when it was energized / unloaded (discharge pressure
should drop and suction pressure should rise.
•
UNIT CONTROL:
Engine and Standby Operation: Pretrip will fail in test 13 and display
“PRETRIP FAIL AND COMPLETED”.
•
RESET CONDITION: Auto Reset if Pretrip is started again or alarm may be manually reset viakey-
pad or by turning the unit off then back on again.
NOTE: Follow the steps below until a problem is found. Once a repair or correction has been made, clear the
alarm(s). (See Note 1 page 7
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2.) Operate the unit through the appropriate modes to see if any active alarm
occurs. Continue with the steps below as necessary.
1
Check wiring to DPT & SPT
a. Verify that correct wires are con-
nected to each transducer.
Plugs to transducers are the same. The correct wire
plug must be connected to the proper transducer.
b. Verify that correct transducer is be-
ing used in each position.
Mechanical connections to transducers are the
same.
The Discharge Transducer should have a RED mark-
ing dot on it.
The Suction Transducer should have a BLUE mark-
ing dot on it.
2
Check for Check UL1 Alarm
Check for alarm 85 or P144.
Alarm conditions must be corrected and the alarm
cleared to continue.
3
Confirm Compressor Suction Pressure Transducer Is Working
a. Check transducer operation
Refer to Section 8.8.8
b. Check Schrader valve fitting under
each transducer
Must not be physically damaged, depressor must
fully open valve to allow pressure to transducer
a. Verify the correct Transducer is in
place.
Verify by part number or colored dot that the correct
Transducer is installed for the SPT.
4
Check System Pressures
Install manifold gauge set and check
and compare compressor discharge
& suction pressures with those
shown on the microprocessor dis-
play.
Suction and Evaporator Outlet pressures must be
above 3 psig (0.2 bar.)
Suction, Evaporator Outlet & Discharge Pressures
must have the same reading on gauges & on micro-
processor display.
NOTE: Microprocessor Suction (CSP and Evapo-
rator (EVOP) pressure readings have a maximum
value of 100 psig (7.5 bar.) The actual pressure
must be lower than 100 psig in order to perform
this test.
5
Check Front Unloader (UL1) Operation - Unit must be running
(See Note 5 page 7
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2)
Check operation of Front Unloader
(UL1).
See Section 8.7.6
Unloader must load and unload properly.
