How To Repair Air Conditioner That's Not Turning On
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How To Repair Air Conditioner That Won't Turn On

About this repair:

  • Rated as REALLY EASY
  • 25 repair stories
  • 5 step by step videos

Electronic Control Board or PCB Assembly

If your air conditioner does not turn on and you have verified that the unit is getting power, you may have a defective control board. Most modern window air conditioners use an Electronic Control Board, or commonly referred to as a PCB, to control the individual components of the unit. If the fan or compressor circuits do not turn on, then the control board may be defective. Check the user manual for proper operation and verify that you are getting power to the unit before condemning the control board. Some control boards may have an internal fuse on them, so check for a blown fuse and replace with the same type and rating if necessary.

Thermostat or Temperature Control

If your air conditioner has a rotary type temperature control or thermostat and does not turn on you may have a defective control. The thermostat control uses a sensor bulb to monitor room air temperature which in turn operates a set of enclosed electrical contacts to supply power to the compressor circuit. The thermostat control senses the room air temperature and turns the compressor circuit on until the set temperature has been reached. Verify that you have power getting to the unit or if your model has an Energy Saver or Fan Only function, verify that the fan will turn on. As you rotate the temperature control or thermostat to a colder temperature setting you should hear a click sound indicating that the contacts close. You can check the thermostat for continuity with a multi-meter as well.

Power Cord

If your window air conditioner won’t turn on, it may be that it is not getting any power. Check the receptacle with a tester or plug in a known working appliance such as a lamp or a fan to verify that the circuit is live. Check the air conditioner power supply cord for any signs of fraying or damage. Newer model units often have a built in circuit breaker in the supply cord, so check to see if that has tripped. If the supply cord appears to be undamaged you can remove the cabinet and with a multi-meter, check the terminal strip where the cord attaches, to verify that you have proper voltage. You should never attempt to repair or modify the supply cord but replace any that you find defective.

Thermistor or Temperature Sensor

Modern window air conditioners often use an Electronic Control Board, sometimes referred to as the PCB, to control the functions of the individual components of the unit. A sensor device called a thermistor is mounted near the front of the evaporator and is used to monitor the room air temperature. This information is sent to the control board where it is processed and used to cycle the compressor on and off to maintain the set temperature. If your air conditioner won’t turn on, you may have a defective temperature sensor. Testing of the sensor will require the technical specifications of the thermistor for your model and a multi-meter. Inspect the control board for any signs of a loose connection to the sensor as well.


Modern window air conditioners that use an Electronic Control often have an internal fuse for protection. If your window air conditioner won’t turn on, it may be that the fuse has blown. First verify that you are getting power to the unit and then unplug the unit and remove the cover. Locate the circuit board and check for a removable fuse. If one is found, look for signs that it has blown or use a multi-meter to check it. If the fuse has blown, replace it only with the proper type and rating.

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