Air Conditioning Troubleshooting

To troubleshoot this type of air-conditioning equipment, a troubleshooting table (Table 15-1) has been provided at the end of this chapter. The general troubleshooting procedures listed in the table are used for hermetically sealed compressors.

Table 15-1 Troubleshooting Hermetic Compressor Type Air-Conditioning Equipment

Trouble Probable Cause Remedy or Repair
Compressor will not start. (No hum.) Open line circuit. Check the wiring, fuses, and receptacle.
Protector open. Wait for reset. Check current drawn from line.
Contacts open on control relay. Check control, and check pressure readings.
Open circuit in the motor stator. Replace the stator or the whole compressor.
Compressor will not start. However, it hums intermittently. Cycles with the protector. Not wired correctly. Check wiring diagram and actual wiring.
Line voltage low. Check line voltage. Find where line voltage is dropped. Correct.
Start capacitor open. Replace start capacitor.
Relay contacts do not close. Check by manually operating. Replace if defective.
Start winding open. Check stator leads. Replace compressor if the leads are OK.
Stator winding grounded. Check stator leads. Replace compressor if leads are OK.
Discharge pressure too high. Remove cause of excessive pressure. Discharge shutoff and receiver valves should be open.
Compressor too tight. Check oil level. Correct the binding cause. If this cannot be done, replace compressor.
Start capacitor weak. Replace the capacitor.
Compressor starts. Motor will not speed up enough to have start winding drop out of circuit. Line voltage low. Increase the voltage.
Wired incorrectly. Rewire according to wiring diagram.
Relay defective. Check operation. If defective, replace.
Run capacitor shorted. Disconnect the run capacitor and check for short.
Start and run windings shorted. Check winding resistances. If incorrect, replace the compressor.
Start capacitor weak. Check capacitors. Replace those defective.
Discharge pressure high. Check discharge shutoff valves.
Check pressure
Tight compressor. Check oil level. Check binding. Replace if necessary.
Compressor starts and runs. However, it cycles on the protector. Low line voltage. Increase the voltage.
Additional current being drawn through the protector. Check to see if fans or pumps are wired to the wrong connector.
Suction pressure is too high. Check compressor. See if it is the right size for the job
Discharge pressure is too high. Check ventilation. Check for over-charge. Also check for obstructions to air flow or refrigerant flow.
Protector is weak. Check current. Replace protector if it is not clicking out at right point.
Run capacitor defective. Check capacitance. Replace if found defective.
Stator partially shorted or grounded. Check resistance for a short to the frame. Replace if found shorted to ground (frame).
Inadequate motor cooling. Correct air flow.
Compressor tight. Check oil level. Check cause of binding.
3 phase line unbalanced. Check each leg or phase. Correct if the voltages are not the same between legs
Discharge valve leaks or is damaged. Replace the valve plate.
Start capacitors burn out. Short cycling. Reduce the number of starts. They should not exceed 20 h.
Prolonged operation with start winding in circuit. Reduce the starting load. Install a crankcase pressure limit valve. Increase low voltage if this is found to be the condition. Replace the relay if it is found to be defective.
Relay contacts sticking. Clean the relay contacts. Or, replace the relay.
Wrong relay or wrong relay setting. Replace the relay.
Wrong capacitor. Check specifications for correct size capacitor.
Be sure the MFD and WVDC are correct for this
Working voltage of capacitor too low. Replace with capacitor of correct WVDC.
Water shorts out terminals of the capacitor Place capacitor so the terminals will not get wet.
Run capacitors burn out. They spew their contents over the surfaces of anything nearby. This problem can usually be identified with a visual check. Excessive line voltage. Reduce line voltage. It should not be over 10% of the motor rating.
Light load with a high line voltage. Reduce voltage if not within 10% overage limit.
Voltage rating of capacitor too low. Replace with capacitors of the correct WVDC.
Capacitor terminals shorted by water. Place capacitor so the terminals will not get wet.
Relays burn out. Low-line voltage. Increase voltage to within 10% of limit.
High-line voltage. Reduce voltage to within 10% of the motor rating.
Wrong size capacitor. Use correct size capacitor. The proper MFD rating should be installed.
Short cycling. Decrease the number of starts per hour.
Relay vibrating. Make sure you mount the relay rigidly.
Wrong relay. Use the recommended relay for the compressor motor.

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