How to Fix an Air Conditioner Coils That are Icing Over

Your air conditioner coils may be icing up because of inadequate air flow, stemming from a dirty or clogged air filter. Air from the room flows over the evaporator coils to be cooled and then back into the room. If the air flow is restricted, it can lead to a frost or ice buildup over the coils. This problem will not sort itself out as the buildup of ice or frost will restrict the air flow even more. Replace the air filter in order to keep the air flowing properly. The filter is usually behind the front grille, and is held in place with plastic tabs.

If your air conditioner coils are icing up, there may be an issue with the temperature control or thermostat. This part monitors the room air temperature and signals the compressor to turn on to begin cooling if necessary. The temperature control will have a sensor bulb, located near the evaporator coils which helps monitor the air temperature. If the temperature control is not functioning properly, it can lead to the compressor running longer than is necessary and cooling the room below ideal temperature. At this point, the evaporator can no longer extract heat from the room which causes the coils to ice over. This is particularly common during periods of intense humidity. Check the sensor bulb for signs of damage such as cracks or bends, and correct placement within the evaporator coil system.

The reason your air conditioner coils are icing up could be inadequate air flow due to a faulty fan or fan motor. In window air conditioner units, the fan pulls air over the evaporator coils to cool it, and then blows it back throughout the room. If the fan is running slowly or not at all, the evaporator coils won’t get enough air and become prone to freezing over. To access the fan and fan motor, unplug the unit and remove the cabinet cover. Try turning the motor manually to see if it rotates easily, and check the fan blades for signs of damage or foreign objects blocking it from turning. If everything appears normal, the fan motor may not be getting power and will need to be tested by a qualified technician.

If your air conditioner coils are icing up, and you have ruled out the air filter and fan motor as the source of the issue, it may be due to a faulty control board or PCB assembly. This part controls the fan motor and compressor circuits, and includes a sensor located near the evaporator coil and signals the compressor to turn on or off. If this sensor is faulty it can result in the compressor running continually and cooling the air to a point that causes the coils to ice or frost over. This is more prone to happen during times of intense humidity. Check the sensor to see if it is damaged before replacing the control board.

The most likely reason your air conditioner coils are icing up is a lack of airflow due to a faulty fan motor capacitor. This part aids the fan in circulating cooled air throughout the room. A sign that the capacitor is not functioning is that the fan motor will make a humming noise or turn very slowly, resulting in restricted air flow and frosted coils. To inspect the capacitor, remove the cabinet cover. Check for signs of wear or damage, and replace the capacitor if it appears damaged.