Window Air Conditioner: Evaporator fins are iced up

The evaporator fins ice up if the compressor runs constantly for one of these reasons: a dirty air filter restricts air flow; the air conditioner is too small for the room; the temperature setting is too cold; a control is defective. See the repairs below to help correct a problem with evaporator finds that ice up.

window air conditioner

These repairs may help solve your window air conditioner problem

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
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 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: 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: dirty air filter, air conditioner is too small for the room, temperature set too cold, control failure
Main causes: clogged drain hole, air conditioner not leveled properly
Main causes: clogged condensate drain, air conditioner not leveled properly, leaky window air seals
Main causes: lack of electrical power, bad electronic control board, wiring failure, bad temperature sensor

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 ambient thermistor

If your window air conditioner isn’t cooling properly, it might need a new ambient thermistor. You can replace it yourself following these instructions.

Repair difficulty
Time required
 45 minutes or less
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 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 common to all room air conditioners

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

September 26, 2019

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