Trane Central Air Conditioner Coil Icing up

The part(s) or condition(s) listed below for the symptom Central air conditioner coil icing up are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.

Most Frequent Causes for Central air conditioner coil icing up

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Cause 1Humidifier Damper is Open

An open humidifier damper will let air bypass the evaporator coil. This loss of air flow can cause the evaporator coil to freeze up. If you have a humidifier on your furnace or air handler, confirm the humidifer damper is in the "summer mode" or closed position.

Cause 2Blower Motor

Blower Motor

Cause 3Blower Wheel and Housing

Blower Wheel and Housing

Cause 4Run Capacitor

Run Capacitor

Cause 5Capacitor


Cause 6Clogged Blower Wheel

Over time the blower wheel can become clogged with dust and debris. This will greatly affect the air flow circulating throughout the home. You can try cleaning the blower wheel with compressed air or with a soft bristle brush. Use caution when trying to clean the blower wheel as the fins are sharp and can be easily damaged. If the blower is damaged it will need to be replaced.

Cause 7Sealed System Problem

If the air flow is good but the evaporator coil is still freezing up, there is likely a leak in the sealed system. If the refrigerant is low the coil will start to freeze up on one side or section. When this happens you may also notice a loss of cooling and water leaking near the coil. If you suspect the system is low on refrigerant it should be checked by a licensed technician.

Cause 8Register is Closed or Only Partially Opened

Some air registers have adjustable louvers that allow the air flow to be restricted or shut off entirely. This would be used to cut off the air flow to a room that isn't being used, or to restrict air flow to one room so more air will flow to the other rooms. If there is low air flow, check that the louvers are fully open.

Cause 9Air Filter

Air Filter

Cause 10Air Flow Problem

Proper air flow is critical for the central air conditioner to work properly. The evaporator needs proper air flow to keep the condensing water from freezing. If the air filter or blower wheel gets clogged, ice can start forming on the evaporator coils, eventually freezing them up. It is recommended to replace the air filter at least every 6 months or sooner depending on the conditions. Avoid covering registers with furniture, rugs, or other items that will restrict the air flow.