Johnson Controls
198
Form 150.72-ICOM6
Issue date: 12/19/2023
Section 9: Service and troubleshooting
Problem
Cause
Solution
Low liquid temp fault
1. Improperly adjusted leaving
chilled liquid temp. cutout (glycol
only).
1. Re-program the leaving chilled liquid temp.
cutout.
2. Micro panel setpoint/range
values improperly programmed.
2. Re-adjust setpoint/range.
3. Chilled liquid flow too low.
3. Increase chilled liquid flow. See
4. Defective LWT or RWT sensor
(ensure the sensor is properly
installed in the bottom of the well
with a generous amount of heat)
conductive compound).
4. Compare sensor against a known good
Temperature sensing device. See
Mp / hpco fault
1. Compressor internal motor
protector (MP) open.
1. Verify refrigerant charge is not low. Verify
superheat setting of 10°F to 15°F (5.6°C to
8.3°C). Verify correct compressor rotation.
Verify compressor is not overloaded.
2. External overload tripped.
2. Determine cause and reset.
3. HPCO switch open.
3. See High Press. Disch. Fault.
4. Defective HPCO switch.
4. Replace HPCO switch.
5. Defective CR relay.
5. Replace relay.
Compressor(s) won’t start
1. Demand not great enough.
1. No problem.
Consult Installation Manual to
aid in understanding compressor operation
and capacity control.
2. Defective water temperature
sensor.
2. Compare the display with a thermometer.
Should be within plus or minus 2 degrees.
See
Table 32 on page 190 for RWT/LWT
temp./voltage table.
3. Contactor/Overload failure.
3. Replace defective part.
4. Compressor failure.
4. Diagnose cause of failure and replace.
Lack of cooling effect
1. Fouled evaporator surface.
Low suction pressure will be
observed.
1. Contact the local Johnson Controls service
representative.
2. Improper flow through the
evaporator.
2. Reduce flow to within chiller design specs.
Operational limitations on page 47
).
3. Low refrigerant charge. Low
suction pressure will be
observed.
3. Check subcooling and add charge as
needed.
Table 35:
Troubleshooting, continued
