Window Air Conditioner: Blows But Doesn't Cool

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.


These repairs may help solve your window air conditioner problem

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:


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

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

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.