Air conditioner (AC) indoor unit or evaporator and wall-mounted

If your air conditioner keeps running when turned off, one or more components may be defective. Ideally, it should shut down completely when turned off; otherwise, it will cause unfavorable temperature conditions and increase your energy bills significantly.

So, here is more on why the air conditioner keeps running when turned off.

Reasons Why The Air Conditioner Keeps Running When Turned Off

Below are the eight most common reasons why your air conditioner keeps running even when it is turned off.

1. Malfunctioning Thermostat

Aside from the air conditioner not turning off, there may be other signs that the thermostat is faulty, including:

  • A discrepancy between the actual temperature and the thermostat reading
  • The air conditioner fails to turn on
  • Unlit or unresponsive thermostat

There are several reasons your thermostat may be malfunctioning, including:

  • Old thermostat. Thermostats have a long lifespan. However, as the years pass by, a bad thermostat may start to exhibit electrical problems and eventually fail. In this case, the thermostat needs to be replaced with a new one.
  • Faulty thermostat temperature sensors. If the temperature sensors are faulty, the thermostat cannot read the temperatures in the room accurately. As such, it will not be able to regulate the running of the air conditioner.
  • Inappropriate location of the thermostat. The installation location of the thermostat is crucial for optimal functioning. It should not be installed at a location that experiences extreme temperatures or extreme changes in temperatures.  For instance, if installed in a location with an extreme draft, it may be interpreted that the surroundings are cool and will turn off the air conditioning unit. On the other hand, if the thermostat is placed in an extremely hot area, e.g., near a boiler tank, it may keep the air conditioner running even when it should turn off.
  • The thermostat temperatures are set too low. If the thermostat temperatures are set way lower than the actual temperature, the unit will keep running as it will never reach the cut point. If you suspect that the thermostat is the issue, start by restarting it. If it does not come on, the batteries may be low and need replacing. Replace the batteries and recalibrate the temperature to ensure it is set within a reasonable range.

Now make sure that the thermostat is installed properly, and it is level. If these steps do not resolve the issue, contact an HVAC technician to diagnose the issue and provide a solution.

2. The Air Conditioner Fan is Set to On

The air conditioner fan works with the other components of your air conditioning system to keep your room cool. However, these parts do not always operate in synchrony. If the air conditioner fan is set to “ON” instead of  “AUTO,” it will keep running even if the rest of the air conditioner is turned off.

To find out if this is the issue with your air conditioning, check your thermostat setting. If it is set to “ON,” it is most likely the issue. If not, there could be another issue, and you should keep reading.

3. Faulty Fan Limit Switch

Even though the fan may be set to “AUTO,” if the fan limit switch is broken or stuck in the override position, the fan will keep running when the air conditioner is switched off. As such, the signal to stop the blower fan is lost in transmission. Reset the fan limit switch to resolve this issue.

4. Faulty Electronic Control Board (PCB Assembly)

air conditioner keeps running when turned offIn addition to a faulty thermostat, you should also consider a faulty control board. The electronic control board is at the center of your AC unit. It transmits signals and information from one component to another.

For instance, when the temperatures are high, the temperature sensor transmits the information to the electronic board, which is transmitted to the cooling system. If the PCB is broken, it does not transmit the information.

Even if you shut the unit down, it will keep operating. You need a specialist to confirm that the electronic control board is broken. Depending on the extent of the damage, you may need to replace the entire AC unit.

5. Short Circuit

There might be a short circuit in your air conditioner’s electrical system if there has been a recent spike in voltage in your house in the recent past. Did you experience a blackout recently? Or have you heard people in your neighborhood complaining about electrical damage to their electronics?

Your AC unit may have short-circuited. As a result, it is not able to transmit electrical signals to the various AC components. You will need an HVAC specialist to handle the issue.

6. Defective Relay Switch

The primary role of a relay switch in an air conditioner is to open and close the electrical circuits. If it is broken or stuck, it inhibits communication between the thermostat and the fan. As a result, when you turn off the AC system, the fan will continue to run.

7. Extremely High Temperatures

If your AC system exhibits issues with turning off in the height of summer, it might be struggling to keep up with the cooling demands of your house. Or, it may have a lower cooling capacity than need be.

To determine whether this is the case, set the thermostat temperatures higher by 5-10°F, then shut off the unit. If it shuts down completely, it is evident that it is overworking, and you need to replace it with a bigger one.

If your air conditioner turns off, contact an HVAC specialist immediately. Since there are many reasons why the air conditioner does not turn off, you may find it difficult to diagnose it accurately. An HVAC technician will easily point out the cause and resolve the issue promptly.

8. Dirty Condenser Coils

An air conditioner operates such that hot air passes over the evaporator coils where it is extracted. The refrigerant passes through the lines into the outdoor unit. The refrigerant is pressurized by a compressor and is then pushed through the condenser coils, where it releases heat.

If the condenser and condenser coils are covered with grime and dirt, they inhibit the transmission of the refrigerant, limiting the unit’s ability to cool the surroundings. As a result, the air conditioner has to work longer and harder to keep the room cool.


There is a wide range of reasons that could cause an air conditioner to keep running when turned off. The issue signals that there is definitely an issue with one or more components of the air conditioner unit. However, it can be difficult to identify the specific cause on your own if you aren’t familiar with the components of your HVAC system.

Therefore, contact an HVAC specialist to diagnose the cause and resolve it appropriately. Some issues are minor and require repair or replacement of the particular component, while others require replacing the entire HVAC system.

Ready to look for a new AC? Read our review of the Best Air Conditioners for 2021 to find the best for your home.