7−94
62-11389
Alarm
NO.
Steps Alarm/Cause Corrective Action
P191 CHECK UL2
• TRIGGER–ON: The pressure differential between suction and discharge pressures did not change
as expected when the Rear Unloader (UL2) 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 via
keypad 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 7−2.) . 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 UL2 Alarm
Check for alarm 86 or P164 Alarm conditions must be corrected and the alarm
cleared to continue
3 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.
4 Check Rear Unloader (UL2) Operation - Unit must be running. (See Note 5 page 7−2)
Check operation of Rear Unloader
(UL2)
See Section 8.7.6.
Unloader must load and unload properly.
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