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In the
Heat Pretrip
Mode, the unit will operate in four cylinder Low Speed Heat. The System will check for a rise in
compressor discharge pressure, fan clutch operation and SV1 operation. Appropriate alarms will be displayed if
any problem is detected. Test 4 in Heat Pretrip may last up to 12 minutes depending on ambient and compartment
temperature and unit condition. During periods when discharge pressure is being read, SV2 may pulse.
Test 5 - UL2 (Rear) Unloader -
With the unit still running the same as it was in Test 4, the operation of unloader
UL2 is tested. If suction and discharge pressures do not change as expected when UL2 is energized and de-ener-
gized, the P00191 - “CHECK UL2” alarm will be displayed. Test 5 will last about 20 seconds.
Test 6 - UL1 (Front) Unloader -
With the unit still running the same as it was in Test 5, the operation of UL1 is
tested. If suction and discharge pressures do not change as expected when UL1 is energized and de-energized,
the P00178 - “CHECK UL1” alarm will be displayed. Test 6 will last about 20 seconds.
Test 7 - Engine Low Speed -
The control system verifies that engine is in the low speed range. If the engine is not
operating in the low speed range, the P00174 - “CHECK LOW SPEED RPM” alarm will be activated.
Test 8 - Engine High Speed -
The engine switches to high speed. The control system verifies that engine is in the
high speed range. If the engine is not operating in the high speed range, the P00175 - “CHECK HIGH SPEED
RPM” alarm will be activated.
Test 9 - Engine Low Speed 2 -
The engine switches back to low speed. The control system verifies that engine
returns to the low speed range within 10 seconds. If not, the P00174 - “CHECK LOW SPEED RPM” alarm will be
activated.
Test 10 - Check Suction Modulation Valve (CSMV) -
This test is run to ensure that the CSMV is opening and
closing properly. If suction pressure doesn’t change as expected with CSMV closed, then the P00180 - “CHECK
SUCTION MOD VALVE” alarm will be displayed.
Test 11 - EVXV -
This test is an operational check of the EVXV. If evaporator outlet pressure doesn’t change as
expected with the EVXV closed then the P00177
−
“CHECK EVAP SUPERHEAT” alarm will be displayed.
Test 12 - SV1 -
The test continues with the unit running in two cylinder low speed cool, SV1 is energized and de-
energized. If the valve does not operate correctly, the P00182 - “CHECK SV1 VALVE” alarm will be displayed. This
test may last up to three minutes.
Test 13 - Check SV4
NOTE
If ambient temperature is above 100°F (37.8°C) this test will not be performed.
With the unit running in two cylinder, low speed heat, SV4 will be energized and de-energized. If the valve does not
operate correctly, the P00181 - “CHECK SV4” VALVE alarm will be displayed. This test may last up to eight min-
utes.
Test 14 - Low Side Pump Down -
With the unit running in two cylinder low speed, SV2 and SV4 will be closed to
pump the low side of the unit down. If the system cannot obtain the required suction pressure, the P00165 - “CAN-
NOT PUMP DOWN” alarm will be displayed.
Test 15 - Pressure Hold Check -
The unit will shutdown, and check for pressure equalization between the high
and low sides. If any leakage is detected, the P00202 - “HIGH SIDE LEAK” alarm will be displayed. This test will
last one minute.
Test 16 - Check Discharge Check Valve -
With the unit off, the discharge check valve is checked for leakage. If
any leakage is detected, the P00203 - “CHK DISCHARGE CHECK VALVE” alarm will be displayed. This test will
last 40 seconds.
Test 17 - Check for Other Alarms -
The alarm list is checked for any non-pretrip alarms that may have occurred
during the Pretrip test. If any operational alarms occurred, Pretrip will show FAIL, and the technician will need to
review the alarm list and take necessary and appropriate action to clear them. This test will last about five seconds.
Pretrip Termination:
When the Pretrip cycle is completed, the unit will return to normal temperature control operation. “PRETRIP PASS”
will be displayed until the operator presses the EXIT key. In the event that the Pretrip test activates an alarm(s),
either “PRETRIP FAIL & COMPLETE” (if the entire Pretrip cycle was completed), or “PRETRIP FAIL IN TEST XX”,
(if the Pretrip cycle was aborted by an alarm before it was completed) will be displayed.
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