Nor-Lake Refrigeration Systems - Manual (Page 23)

09/14 Rev. E 101628 23
SERVICE DIAGNOSIS CHART
Symptoms Possible Cause
Compressor hums, but will not start 1. Improperly wired
2. Low line voltage
3. Defective run or start capacitor
4. Defective start relay
5. Unequalized pressures on PSC motor
6. Shorted or grounded motor windings
7. Internal compressor mechanical damage
Compressor will not run, doesn’t try to start (no hum) 1. Power circuit open due to blown fuse, tripped circuit breaker
or open disconnect switch
2. Compressor motor protector open
3. Open thermostat or control
4. Burned motor windings, open circuit
Compressor starts, but trips on overload protector 1. Low line voltage
2. Improperly wired
3. Defective run or start capacitor
4. Defective start relay
5. Excessive suction or discharge pressure
6. Tight bearings or mechanical damage in compressor
Unit short cycles 1. Control differential too small
2. Shortage of refrigerant
3. Discharge pressure too high
4. Discharge valve leaking
Starting relay burns out
1. Low or high line voltage
2. Short cycling
3. Improper mounting of relay
4. Incorrect running capacitor
5. Incorrect relay
Contacts stick on starting relay 1. Short running cycle
2. No bleed resistor on start capacitor
Starting capacitors burn out 1. Compressor short cycling
2. Relay contacts sticking
3. Incorrect capacitor
4. Start winding remaining in circuit for prolonged period
Running capacitors burn out 1. Excessively high line voltage
2. High line voltage, light compressor load
Head pressure too high
1. Refrigerant overcharge
2. Air in system
3. Dirty condenser
4. Malfunction of condenser fan (air cooled)
5. Restricted water flow (water cooled)
6. Excessive air temperature entering condenser
7. Restriction in discharge line
Head pressure too low 1. Low ambient temperature (air cooled)
2. Refrigerant shortage
3. Damaged valves or rods in compressor
Refrigerated storage temperature too high
1. Restricted strainer, drier or expansion device
2. Improperly adjusted expansion valve
3. Iced or dirty evaporator coil
4. Compressor malfunctioning
5. Thermostat setting incorrect
Loss of oil pressure 1. Loss of oil from compressor due to:
a. Oil trapping in system
b. Compressor short cycling
c. Insufficient oil in system
d. Operation at excessively low suction pressure
2. Excessive liquid refrigerant returning to compressor
3. Malfunctioning oil pump
4. Restriction in oil pump inlet screen