5 Reasons Why Window Air Conditioner Keeps Running When Turned Off

5 Reasons Why Window Air Conditioner Keeps Running When Turned Off

There are three problems with window air conditioners which irritate their users the most. The most frustrating among them – especially because it weighs heavily on your electricity bill – is when the window air conditioner keeps running when turned off.

You have switched it off from the remote, turned its thermostat to the extreme left and even smashed your hand against its control panel. Still, as if to test the limits of your patience, the air conditioner keeps on churning out cool air. That too when your room temperature has already become comfortable.

Want to get rid of this problem? Then keep on reading.

Why Window Air Conditioner Keeps Running When Turned Off?

Listed below are five common reasons as to why that might be happening:

1. Problem with its PCB Assembly

Problem with its PCB Assembly

Almost all modern window air conditioners have an Electronic Control board, also referred to as PCB, that is responsible for controlling the functions of their individual components. It consists of a thermistor device that monitors your room temperature and then sends that info to the control board.

On receiving the information, output relays on the board issue commands to the fan and the compressor circuits. Provided your room temperature has already reached the setpoint, the output relay will tell the fan and the compressor to shut off. Conversely, it will tell them to keep going.

However, if either the compressor or the fan (or both) keep on running even after the setpoint temperature has been reached, the problem might be with the output relay. Such a scenario would require you to replace the complete control board.

That being said, there are some window air conditioners whose relay board is separate from their Electronic Control Board. If that’s the case with your air conditioner, you might have to use a multimeter to inspect the sensor for any signs of damage or poor connection before replacing the board.

2. Problem with the thermostat

If your window air conditioner keeps running when turned off, and continues to churn out cold air, there might be an issue with its thermostat. Also known as temperature control in common language, the thermostat supplies power to the compressor circuit using its internal electrical contacts.

It is also connected to a bulb sensor and a capillary tube, devices that monitor room air temperature via their connection with the evaporator coil. As the sensor senses a drop in temperature, it should ideally open the switch contacts and cut off the power supply to the compressor.

That is what should happen in an ideal scenario. However, if the connections are stick closed or weld, the compressor may continue to run even after the sensor has issued the command that the desired room temperature has been achieved.

You need to inspect the sensor bulb to rule out this option. If you find out that the sensor is working fine – but the compressor is still running after you have turned off the window air conditioner – then it’s time to repair the thermostat.

3. Problem with the temperature sensor

As stated earlier, all window air conditioners come with a temperature sensor (thermistor). This device is mounted on the room-facing side of the evaporator, though you can’t see it since it’s hidden inside the front-facing casing of the air conditioner.

The main purpose of the sensor, as its name implies, is to measure your room temperature. It then uses that measurement to tell the compressor whether to keep running (if the desired temperature hasn’t been reached yet) or to shut down (if your room is already cold enough).

Unfortunately, we have seen some window air conditioners whose temperature sensor went awry. It is no longer able to measure your room temperature and the compressor, which relies on the sensor to turn on/off, keeps on churning out cold air.

To test the sensor, you need two things: technical specs of the thermistor of your window air conditioner and a multi-meter. Once you have them, inspect the control board. It may happen that the sensor is working fine, but only its connection with the control board has become loose.

4. It’s too hot outside

It’s too hot outside

Provided you have installed an undersized window air conditioner for the space you want it to cool, it will keep on running even when you don’t want it to. Know why? Because the system won’t get to the setpoint you set the thermostat at. This issue mainly arises when it’s too hot outside.

If that’s indeed the case, you have two solutions: invest in a bigger-size window air conditioner or wait until the weather outside drops a little. Regardless of the option you might choose, never forget to maintain your air conditioner regularly. That would put less load on the compressor.

5. Short-circuiting

In the days when your air conditioner turned on/off normally, were there instances when your home witnessed spikes in electricity? Heard a neighbor complaining that some of their electrical devices were burnt because of the increase in voltage?

If your answer to any of these questions is in the affirmative, then your air conditioner might have short-circuited. Now, when you turn it on or off, the commands aren’t getting to the blower – because the wires that connect the blower to the thermostat might have burnt. You can’t fix this issue on your own and might have to call a local HVAC company.


There are five main reasons why your air conditioner might keep running even when you have tried to turn it off. They include a potential problem with its PCB assembly, an issue with the thermostat, the temperature control unit or thermistor going awry, the weather outside being too hot or a short-circuiting in the internal wires of your air conditioner.

If you ask us, we recommend that you hire an expert to fix any of these issues. Sure, some of you might have enough technical knowledge to fix the problem on your own, but it’s always better to leave the technical stuff to the experts. Their expertise would make sure that once they’ve resolved the issue, it won’t happen for quite some time. Please get in touch if you want to know more.

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