The evaporator coil helps cool the air coming into the air conditioner. It needs to be cold in order to perform its basic job function, but it’s not supposed to be frozen or iced over. If you can see a layer of frost or ice on your evaporator coil, it could indicate a more serious problem with your AC unit. Evaporator coil freezing can be caused by:A lack of airflow around the coil, often because of a filter that has become clogged by dust and debrisLow refrigerant levels, which can occur naturally over timeTrying to run the temperature in your home too cold, which results in the air conditioner working too hard