CGAT-IOM01-EN
15
Symptom
Recommended action
A. Compressor neither starts nor hums.
Probable Cause
1. No power
a. Check for disconnect switch open.
b. Check for blown fuse
2. No call for cooling
a. Check for defective thermostat or
b. Broken or improper control wiring
3. Unit locked out by reset relay
a. Check for excessive discharge pressure
b. Check for defective thermostat
4. Compressor contactor will not close
a. Check for open reset relay
b. See for defective thermostat
5. Compressor winding thermostat open
a. Check compressor amp. Draw
b. See compressor winding thermostat open
B. Compressor hums, but will not start
1. Low voltage at compressor
a. Check for low fine voltage
b. Check for defective compressor contactors
2. Defective compressor
a. Check fro open motor winding
b. Check for excessive amp. draw on all phases.
C. 2nd. stage compressor fails to start
1. Time delay contacts fail to close
Replace time delay relay
2. No call for cooling
a. Check for defective thermostat
b. Check for improper control wiring
3. Locked out by reset relay
a. see Symptom A.
4. Compressor contactor will not close
a. see Symptom A.
D. Compressor runs continuously
1. Unit undersized for load
a. Check cause of excessive load.
2. Thermostat setpoint too low
a. Re-adjust thermostat setting.
3. ”Welded” contacts on compressor contactor
a. Repair or replace contactors.
4. Leaky valves in compressor
Replace compressor
(indicated by abnormally low discharge and
high suction pressure)
5. Refrigerant shortage (as indicated by reduced
Find and repair leak. Recharge system.
capacity, high superheat, low subcooling and
low suction pressure)
E. Compressor motor winding thermostat open
1. Excessive load on evap.
a. Check for excessive water flow.
b. Check for high return water temp.
2. Lack of motor cooling
a. Check for improper expansion valve setting or faulty
expansion valve.
b. Check for restriction in liquid line.
3. Improper voltage at compressor
a. Check for low or imbalanced line voltage, loose power
wiring or defective compressor contactor.
Trouble Shouting
