Air Conditioner Compressor Issues: Diagnosis & Repair Guide

Quick answer

If your air conditioner compressor won't start, first check the power supply and thermostat settings. If the issue persists, inspect the capacitor and contactor for damage. Replace faulty parts as needed, and call a professional if the compressor is seized or making loud noises.

Confirm the symptom

• Compressor doesn't start when AC is turned on
• AC runs but doesn't cool properly
• Loud or unusual noises from the outdoor unit
• Compressor starts then immediately shuts off
• High energy bills with no apparent cause

Tools and prep

• Voltage tester
• Screwdrivers (flathead and Phillips)
• Multimeter
• Replacement capacitor (if applicable)
• Safety gloves and goggles
• Service manual for your AC unit
• Turn off power to the AC unit at the circuit breaker

Step-by-step troubleshooting

1. Check Power Supply
   Do: Verify the circuit breaker hasn't tripped and the disconnect switch is on.
   Observe: Power is restored to the unit.
   Means: The issue may be resolved if power was interrupted.
   Next: If power is on but the compressor still doesn't work, proceed to the next step.
2. Inspect Thermostat
   Do: Ensure the thermostat is set to 'Cool' and the temperature is lower than the room temperature.
   Observe: Thermostat settings trigger the AC to run.
   Means: Incorrect settings can prevent the compressor from starting.
   Next: If the thermostat is set correctly, move to the next step.
3. Check Capacitor
   Do: Use a multimeter to test the capacitor for proper voltage.
   Observe: Capacitor reads within the manufacturer's specifications.
   Means: A faulty capacitor can prevent the compressor from starting.
   Next: Replace the capacitor if it's damaged or not holding charge.
4. Examine Contactor
   Do: Look for signs of wear or burning on the contactor inside the condenser unit.
   Observe: Contactor shows visible damage or arcing.
   Means: A faulty contactor can interrupt power to the compressor.
   Next: Replace the contactor if it's damaged.
5. Listen for Unusual Noises
   Do: Turn the AC on and listen for loud or grinding noises from the compressor.
   Observe: Unusual noises are present during operation.
   Means: Loud noises may indicate a seized or damaged compressor.
   Next: If noises are present, stop the unit and call a professional.
6. Check Refrigerant Levels
   Do: Inspect for refrigerant leaks using a leak detector or look for oil stains around the coils.
   Observe: Refrigerant leaks or low levels are detected.
   Means: Low refrigerant can cause the compressor to work harder and overheat.
   Next: Refrigerant issues require professional handling due to environmental regulations.
7. Test Compressor Windings
   Do: Use a multimeter to test the resistance of the compressor windings.
   Observe: Resistance readings are outside the normal range.
   Means: Faulty windings can prevent the compressor from functioning.
   Next: If windings are faulty, the compressor may need to be replaced.
8. Inspect for Overheating
   Do: Check the compressor's temperature after running the AC for a while.
   Observe: Compressor is excessively hot to the touch.
   Means: Overheating can be a sign of internal failure or electrical issues.
   Next: Turn off the unit and allow it to cool. If overheating persists, consult a professional.

Common causes

Parts matching

Common parts needed for air conditioner compressor issues include:

• Capacitor: Replaces the starting and running capacitor for the compressor.
• Contactor: Sends power to the compressor and can wear out over time.
• Thermostat: Controls the temperature and signals the compressor to start.
• Air Filter: Keeps the system clean and prevents overheating.
• Cleaning Kit: Removes debris from condenser coils to improve efficiency.

Always match the part specifications to your AC unit's model and size for proper function.

When to call a professional

• The compressor makes loud or grinding noises.
• The compressor is completely unresponsive after checking power and basic components.
• You detect refrigerant leaks or smell a chemical odor.
• The unit is overheating and shutting down repeatedly.
• You suspect internal compressor failure or electrical issues beyond basic troubleshooting.

FAQ

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