Air Conditioner Does Not Shut Off

If your air conditioner does not shut off, the problem could be caused by a faulty thermostat, stuck contactor, dirty air filter, or a malfunctioning control board. Before replacing any parts, inspect the most common causes listed below.

Safety Notice: Always turn off power to the air conditioner before servicing it. If the unit continues running after being turned off at the thermostat, disconnect power at the circuit breaker to prevent unnecessary wear or damage.

Possible Causes

  • Faulty thermostat
  • Stuck contactor
  • Dirty or clogged air filter
  • Failed control board
  • Incorrect thermostat settings
  • Low refrigerant level
  • Oversized or undersized air conditioner
  • Loose or damaged wiring

1. Faulty Thermostat

Most Common Solution

A malfunctioning thermostat may continuously call for cooling, preventing the air conditioner from shutting off even after the desired temperature has been reached.

What to do:

  • Verify the thermostat is set correctly.
  • Lower and raise the temperature setting to test its response.
  • Replace the thermostat if it fails to cycle the system properly.

2. Contactor

The contactor supplies power to the compressor and condenser fan motor. If its contacts become welded together, the outdoor unit may continue running even when the thermostat is off.

What to do:

  • Turn off power to the unit.
  • Inspect the contactor for burned or welded contacts.
  • Replace the contactor if it is stuck closed.

3. Dirty or Clogged Air Filter

A clogged air filter restricts airflow, making it difficult for the system to reach the desired temperature. As a result, the air conditioner may appear to run continuously.

What to do:

  • Remove and inspect the air filter.
  • Replace the filter if it is dirty.
  • Restore power and monitor the system's operation.

4. Control Board

A failed control board can continuously energize the cooling system, preventing the air conditioner from shutting off.

What to do:

  • Inspect the control board for burned components or visible damage.
  • Replace the board if it is defective after ruling out the thermostat and contactor.

5. Incorrect Thermostat Settings

If the thermostat is set too low or the fan is set to On instead of Auto, the system may seem like it never shuts off.

What to do:

  • Verify the thermostat is set to Cool mode.
  • Change the fan setting from On to Auto.
  • Adjust the temperature to an appropriate setting.

6. Low Refrigerant Level

Low refrigerant reduces cooling efficiency, causing the air conditioner to run much longer in an attempt to reach the thermostat setting.

What to do:

  • Inspect for ice on the evaporator coil or refrigerant lines.
  • Have the system checked for leaks.
  • Repair the leak before recharging the refrigerant.

7. Incorrectly Sized Air Conditioner

An air conditioner that is too small for the space may run continuously because it cannot keep up with the cooling demand.

What to do:

  • Verify the unit is properly sized for your home.
  • Improve insulation or reduce heat gain if necessary.
  • Consult an HVAC professional if sizing is a concern.

8. Wiring

Loose or damaged wiring can interfere with the control signals sent between the thermostat and the air conditioner, causing continuous operation.

What to do:

  • Disconnect power to the unit.
  • Inspect accessible wiring and electrical connections.
  • Tighten loose connections.
  • Replace damaged wiring before restoring power.

Need Help Finding the Correct Part?

If you need help identifying the correct replacement part, send us your complete air conditioner model number and a clear photo of the appliance identification label before placing your order. Our team will verify compatibility and help ensure you receive the correct replacement part the first time.