- 1). Shut off the electrical power to the air conditioning unit and the outdoor condenser coil if applicable. Most whole-house systems have two separate power supplies for the larger unit. Unplug a window from the wall outlet. Allow the ice buildup to thaw from the coils. Do not attempt to thaw the ice with an artificial heat source.
- 2). Clean the evaporator drain pan to ensure the water is draining from the unit. Plugged drains can cause water to back up around the indoor coil, causing ice to form prematurely.
- 3). Remove the indoor air filter from the main return duct on whole-house systems or from the front of the window unit. Once the coil is dry, clean the aluminum fins with a vacuum cleaner and brush attachment. Dirty evaporator fins reduce airflow across the coil, increasing chances for freezing. Inspect and clean the blower fan blades for accumulation of dust and dirt. Dirty fan blades reduce the amount of air that passes through the indoor coil.
- 4). Replace the old air filter with a new one or clean the window unit filter under a stream of warm water. Allow the filter to dry before turning the indoor unit back on.
- 5). Hose down and clean the outdoor condenser coil. Wash the aluminum fins in a downward motion to remove accumulated dirt and debris. Keep at least a three-foot perimeter around the outdoor coil for good airflow to the coils. You may have to remove the window unit from its installed position to thoroughly clean the coil that sits outside the home.
- 6). Call a certified air-conditioning technician if the problem persists. There are many other possible causes of icing of the coils, most commonly low refrigerant levels, malfunctioning valves or a bad electrical relay. In some cases, special tools are necessary to test and correct the problem.
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