Window Air Conditioner: Running but not cooling

If the window air conditioner's compressor and fans are running but the air conditioner isn't cooling, possible causes include a failed compressor or the lack of refrigerant due to a leak in the sealed system. If the compressor isn't running but the fans work, the start relay or compressor might have failed. A defective electronic control board or control thermostat could prevent the window air conditioner from cooling. See the repairs listed below for help with correcting this problem.

window air conditioner

These repairs may help solve your window air conditioner problem

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
Read more
Replace the window air conditioner compressor

Replace the window air conditioner compressor

The compressor is a pump that compresses the refrigerant-Freon-that's sealed in the window air conditioner. If the compressor doesn't run when activated, have a refrigerator service technician replace it; by law, an EPA-licensed technician must do this repair because it involves Freon.

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 evaporator thermistor

Replace the window air conditioner evaporator thermistor

The evaporator thermistor is a temperature sensor that is mounted on the evaporator. It monitors the temperature of the evaporator to detect excessive frost on the evaporator. The thermistor communicates that temperature to the electronic control board through a wire harness connection. If the evaporator frosts up, the electronic control board will detect the frost according to the temperature communicated through the thermistor. If the thermistor is defective, the electronic control will not properly detect and eliminate the frost. Replace the evaporator thermistor if it doesn't properly detect the evaporator temperature.

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
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How to fix a smelly room air conditioner
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Learn how to remove and prevent odors in a window air conditioner.