York YLAA0041 Installation Operation & Maintenance page 198

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