Once the coil heats up, then it must be kept cool with the help of proper airflow. The coil stays cold when it continuously receives warm air coming out of the home. The process helps maintain its freezing temperature without which the coils will freeze even when the condensed water has not drained completely.
Airflow is blocked because of closed air registers and dirty air filters. These parts of the air conditioner should be checked regularly to make sure the airflow is not blocked. If the fan is not working properly and the refrigerant level is low then it will cause the air conditioner to freeze. The faulty fan means the air cannot move freely. Coils become cold if the refrigerant level goes down.
Air conditioner freeze up is also caused by drainage problems and faulty thermostats. Air conditioner performs cooling operation by condensing water vapor that drain outside. The drain hole will be blocked with the ice if the coils are frozen. In such a condition, the AC unit consumes more electricity because it runs inefficiently.
One way to unfreeze the coil is to use a hair dryer. This trick can be used on a window AC unit. Any blockage of the drainpipe should also be checked. Sometimes debris gets into the drainpipe and blocks it. It must be remembered that compressor can be damaged extensively if the air conditioner is run with frozen coils.
Repair or replacement of this part can be very expensive. If it is not possible to solve the problem of frozen coils by self then it is important to call a professional air conditioner technician.