The part(s) or condition(s) listed below for the symptom Air conditioner coils freezing 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.
If the air filter becomes clogged with dirt, it restricts airflow over the evaporator coils. If the airflow is reduced, the evaporator coils get too cold, which then causes the humidity in the room to condense on the coils and freeze. As frost accumulates on the coils, the frost restricts the airflow even more. Eventually, the entire evaporator coil assembly will frost over, causing the airflow to be completely restricted. If the air filter is dirty, replace it.
If the air conditioner coils are freezing in only one area, there may be a sealed system (or refrigerant) leak. This is normally a very expensive repair. Repairs to the sealed system must only be performed by a licensed technician.