Window Air Conditioner: Won't start

If the window air conditioner has electrical power-the control panel powers up-but the compressor and fans won't run, possible causes include an electronic control failure or a wiring problem. The window air conditioner also won't start if the electronic control detects a component problem such as a defective thermistor. Check the control panel for an error code, which usually indicates which component failed. To decipher an error code, check our error code tables or refer to your owner's manual. Some repairs that could correct the problem are listed below.

window air conditioner

These repairs may help solve your window air conditioner problem

Replace the window air conditioner control thermostat

Replace the window air conditioner control thermostat

Some window air conditioners have an electro-mechanical thermostat instead of an electronic control board to control the on/off cycling of the compressor and fans. Replace the thermostat if it fails to control the compressor and fans properly.

Replace the window air conditioner electronic control board

Replace the window air conditioner electronic control board

The electronic control board regulates the compressor, evaporator fan and condenser fan in the window air conditioner. If the electronic control board doesn't activate those components properly, replace the control board.

How to replace a window air conditioner electronic control board

When a window air conditioner won't cool or won't start at all, the electronic control board might be the problem. This step-by-step repair guide shows how to replace a window air conditioner electronic control board.

Repair difficulty
Time required
 45 minutes or less
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Replace the window air conditioner user interface control board

Replace the window air conditioner user interface control board

The user interface control board in the control panel houses the selection buttons you push. A wire harness connects the user interface control board to the control board. If the selection buttons don't respond when you push them, replace the user interface control board.

How to replace a window air conditioner user interface control board

If the buttons on your window air conditioner don't work or if the control panel doesn't light up, the user interface control board could be the problem. This DIY repair guide explains how to replace a window air conditioner user interface control board in less than 30 minutes.

Repair difficulty
Time required
 30 minutes or less
Read more
Replace the window air conditioner ambient thermistor

Replace the window air conditioner ambient thermistor

The window air conditioner ambient thermistor-also known as a temperature sensor-senses the temperature of the air entering the air conditioner and communicates that temperature to the electronic control board, which cycles the compressor on and off to maintain the set room temperature. The ambient thermistor is attached to the evaporator coil that's behind the air filter, and a wire harness connects the ambient thermistor to the electronic control board. If the ambient thermistor is defective, the electronic control board will not cycle the compressor on and off properly to maintain the room temperature that is set on the control. Replace the ambient thermistor if it doesn't accurately measure the ambient room temperature.

How to replace a window air conditioner ambient thermistor

If your window air conditioner isn't cooling the room very well, the ambient thermistor might be at fault. This DIY repair guide explains how to replace a window air conditioner ambient thermistor with step-by-step instructions.

Repair difficulty
Time required
 45 minutes or less
Read more
Symptoms for window air conditioners

Choose a symptom to see related window air conditioner repairs.

Main causes: dirty air filter, air conditioner is too small for the room, temperature set too cold, control failure
Main causes: lack of electrical power, bad electronic control board, wiring failure, bad temperature sensor
Main causes: bad compressor, lack of refrigerant, bad compressor start relay, electronic control board failure
Main causes: turning the air conditioner off and the back on too quickly, dirty or restricted condenser coil, compressor failure
Main causes: clogged condensate drain, air conditioner not leveled properly, leaky window air seals
Main causes: clogged drain hole, air conditioner not leveled properly
Repair guides for window air conditioners

These step-by-step repair guides will help you safely fix what’s broken on your window air conditioner.

How to replace a window air conditioner user interface control board

Control buttons or lights on the user interface control board can stop working. This repair guide shows how to replace it.

Repair difficulty
Time required
 30 minutes or less
How to replace a window air conditioner condenser fan

If the condenser fan blade is broken or the condenser fan motor won’t run, you can replace the broken parts yourself by following these instructions.

Repair difficulty
Time required
 90 minutes or less
How to replace a window air conditioner electronic control board

The electronic control board is the brain of your window air conditioner. Here’s how to replace it.

Repair difficulty
Time required
 45 minutes or less
Articles and videos for window air conditioners

Use the advice and tips in these articles and videos to get the most out of your window air conditioner.

February 15, 2018
How to maintain your HVAC system video
By Erin Hynes

6 ways to extend the life of your HVAC system.

February 1, 2018
How to read a wiring schematic video
By Erin Hynes

Learn how to decipher symbols so you can buy the right part for your problem.

January 20, 2015
How to fix a smelly room air conditioner
By Erin Hynes

Learn how to remove and prevent odors in a window air conditioner.