AC Compressor Not Working: Causes, Fixes, and What to Do

If your AC compressor is not working, the problem is often a failed capacitor, contactor, power issue, or internal compressor failure.

The compressor is the heart of your central air conditioning system. If it is not running, your AC cannot cool your home—no matter what the thermostat or indoor unit is doing.

These issues often cause AC Not Turning On or AC Not Cooling. This guide explains how to identify compressor problems, what you can safely check yourself, and when it’s time to call a professional.

Quick Answer

If your AC compressor is not working, check the thermostat, breaker, and outdoor disconnect first. If the unit hums, clicks, or does nothing at all, the problem is often a failed capacitor, contactor, or the compressor itself.

Bottom Line: Compressor problems can range from inexpensive fixes like a capacitor to costly replacements—diagnosing the cause early is key.

See all problems: AC Not Working Troubleshooting Guide

Start With These Quick Checks

Begin with these simple checks before assuming a major failure.

• Set the thermostat to COOL and lower the temperature
• Check the circuit breaker for the outdoor unit
• Inspect the disconnect box near the condenser
• Listen for sounds from the outdoor unit (clicking, humming, or silence)
• Make sure the indoor unit is running

Common Causes of an AC Compressor Not Working

If the compressor does not start or run properly, use this table to identify the likely cause.

How to Fix an AC Compressor That’s Not Working

Follow these steps to diagnose and potentially fix the problem.

1. Check Power to the Unit

The compressor will not run if the unit has no power.

• Check the main electrical panel
• Reset any tripped breakers
• Inspect the outdoor disconnect box

2. Listen for Warning Sounds

The sounds your AC makes can help identify the problem.

• Clicking: Possible contactor issue
• Humming: Likely capacitor problem
• Silence: Possible power or thermostat issue

3. Check the Thermostat

If the thermostat is not sending a signal, the compressor will not start.

• Replace batteries if needed
• Confirm COOL mode and settings

See: Thermostat Troubleshooting Guide

4. Inspect the Capacitor and Contactor

These are common failure points in outdoor units.

• A failed capacitor prevents the compressor from starting
• A bad contactor prevents power from reaching the compressor

Safety Note: The capacitor and contactor carry high voltage and can retain electrical charge even when power is off. Do not touch or test these components unless you are trained.

5. Check for Refrigerant Issues

If refrigerant levels are low, the system may shut down or fail to cool properly.

This requires professional diagnosis and repair.

When to Call a Pro

Compressor-related problems often require professional service. Call an HVAC technician if:

• The compressor does not start after basic checks
• You hear humming, buzzing, or repeated clicking
• The breaker trips repeatedly
• You suspect low refrigerant or a leak
• The compressor appears to have failed completely

Repair or Replace?

Whether to repair or replace depends on the cause and the age of the system.

See: Central AC Repair Cost Guide

See: Repair vs Replace Central AC

FAQs

How do I know if my AC compressor is bad?

Signs include no cooling, loud noises, tripped breakers, or the outdoor unit not running.

Can a bad capacitor stop the compressor?

Yes. The capacitor provides the boost needed to start the compressor.

Is it expensive to replace a compressor?

Yes. Compressor replacement can cost $1,200 to $2,500 or more.

Should I repair or replace a bad compressor?

If the system is older, replacement is often the better investment.

NEXT SEE

• Central AC Not Working
• AC Not Turning On
• Central AC Not Cooling
• AC Blowing Warm Air
• Central AC Repair Cost Guide