Search guides

Fix a condenser that will not run

We'll confirm the symptom, rule out thermostat and power, then isolate the cause—capacitor, contactor, or compressor—or tell you when to call a pro for refrigerant work.

Troubleshooting · Home maintenance
15–45 min
What you'll need
  • Multimeter (for capacitance and voltage tests)
  • Screwdriver set (Phillips and flathead)
  • Replacement run capacitor or contactor (if tests show a fault)
Step 1 of 6

Quick triage — pick your path

Get started

Choose the option that matches what you see. You can jump straight to that section.

Show full guide

Steps

Goal: Confirm the symptom, rule out thermostat and power, then isolate the cause.

  • Set the thermostat to Cool. Go outside to the condenser unit.
  • Good: The outdoor unit is silent when it should run. Proceed to Check thermostat and power.
  • Bad: The fan and compressor run—condenser is working; different problem. See When to get help.

Check thermostat and power

Goal: Rule out thermostat and power.

  • Confirm the thermostat is set to Cool and the temperature is below the room temperature.
  • Check the circuit breaker and the disconnect switch near the condenser. Reset or turn on if needed.
  • Good: Thermostat correct, breaker and disconnect on. Proceed to Check capacitor and contactor.
  • Bad: Breaker trips immediately—do not reset again. Call a technician.

Check capacitor and contactor

Goal: Test and replace the run capacitor or contactor if faulty.

  • Turn off power at the circuit breaker and disconnect. Open the condenser access panel.
  • Locate the run capacitor. Check for bulging, leaking, or burn marks. Test capacitance with a multimeter. Replace with an exact match if faulty. Discharge the capacitor before touching it.
  • Locate the contactor. Inspect for pitting, burning, or stuck contacts. When the thermostat calls for cooling, the coil should pull in. Replace if faulty.
  • Good: Capacitor or contactor replaced and the condenser runs.
  • Bad: Both check out but the condenser still does not run—call a pro for compressor or refrigerant work. Do not add refrigerant yourself.

Retest the condenser

Goal: Confirm the condenser runs after replacing components.

  • After replacing the capacitor or contactor, restore power and set the thermostat to Cool.
  • Confirm the condenser fan and compressor run and cool air comes from the supply vents.
  • Good: Outdoor unit runs and cool air flows.
  • Bad: Condenser still does not run—call a technician.

When to get help

Refrigerant work requires EPA certification. Do not add refrigerant yourself.

Call an HVAC technician if:

  • The capacitor and contactor check out and the condenser still does not run.
  • The compressor or fan motor has failed.
  • You suspect a refrigerant leak.
  • You are not comfortable working with electricity.

Verification

  • The condenser fan and compressor run when the thermostat calls for cooling.
  • The outdoor unit runs quietly with no unusual noises.
  • Cool air comes from the supply vents.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify the condenser does not run when the thermostat calls for cooling.
  2. Thermostat and power Check thermostat setting, circuit breaker, and disconnect.
  3. Run capacitor Test and replace capacitor if faulty.
  4. Contactor Check contactor for pitting, burning, or stuck contacts; replace if faulty.
  5. Compressor or fan motor Technician can test; compressor or fan replacement may be needed.
  6. Call a pro Refrigerant work, compressor failure, or capacitor/contactor good but unit still does not run—licensed pro only.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Whether the indoor blower runs
  • Thermostat setting
  • Circuit breaker and disconnect status
  • Capacitor and contactor test results
  • Steps already tried

Does the condenser not run when the thermostat calls for cooling?

Set the thermostat to Cool. The outdoor fan and compressor should run. If the unit is silent, the condenser is not running.

Set the thermostat to Cool. Go outside to the condenser. Good: outdoor unit is silent when it should run—condenser not running. Bad: fan and compressor run—condenser is working; different problem.

Yes No

You can change your answer later.

Is the thermostat set to Cool and is power on?

Thermostat must be on Cool. Circuit breaker and disconnect must be on.

Confirm thermostat is set to Cool and temperature is below room temp. Check the circuit breaker and disconnect switch near the condenser. Good: thermostat correct, breaker and disconnect on. Bad: breaker trips immediately—do not reset; call a technician.

Yes No

You can change your answer later.

Does the run capacitor test good?

The run capacitor helps the fan and compressor start. A failed capacitor prevents the condenser from starting.

Turn off power and disconnect. Open the condenser panel. Locate the run capacitor. Check for bulging, leaking, or burn marks. Test capacitance—compare to µF rating. If more than 10% off or damaged, replace with an exact match. Good: capacitor in spec or replaced. Bad: capacitor failed—replace and retest.

Yes No

You can change your answer later.

Replace capacitor and test

Replace the run capacitor with an exact match. Restore power and test. The condenser should run if the capacitor was the only fault.

Done

Does the contactor close when the thermostat calls for cooling?

The contactor sends power to the compressor and fan. Pitted or stuck contacts prevent the condenser from running.

Turn off power. Locate the contactor. Inspect for pitting, burning, or stuck contacts. When the thermostat calls for cooling, the coil should pull in and contacts close. Replace if faulty. Good: contactor closes and condenser runs. Bad: contactor faulty—replace. If good but condenser still does not run—call a pro for compressor or refrigerant work.
Question

Does the contactor close and condenser run?

Continue

You can change your answer later.

Call a technician

Refrigerant work requires EPA certification—do not add refrigerant yourself. Call an HVAC technician if the capacitor and contactor check out and the condenser still does not run, if the compressor or fan motor has failed, if you suspect a refrigerant leak, or if you are not comfortable working with electricity.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a condenser not run?
Common causes: thermostat not set to Cool, tripped circuit breaker, failed run capacitor, faulty contactor, or a dead compressor. Check thermostat and power first, then the capacitor and contactor. Refrigerant issues require a licensed technician.
Can I replace a condenser capacitor myself?
Yes, if you are comfortable with electricity. Turn off power at the circuit breaker and disconnect. Discharge the capacitor before touching it. Match the microfarad (µF) rating and voltage exactly. Wrong values can damage the compressor or fan motor.
When should I call an HVAC technician for a condenser that will not run?
Call a pro for refrigerant work—adding or repairing refrigerant requires EPA certification. Call if the capacitor and contactor check out and the condenser still does not run, if the compressor is suspected failed, or if you are not comfortable working with electricity.

Rate this guide

Was this helpful?

Continue to