Airflow constriction due to dirt or grime may cause a window air conditioner to run hot. Storage and disuse may cause dirt to accumulate on the air conditioning coils and in the filter, causing hot exhaust air to leak back through the air ducts.
Dirty air filters can be cleaned using running water in most modern units. Specialized fin combs can also be used to remove accumulated dirt and straighten out evaporator and condenser coils, resulting in more efficient cooling. If such superficial cleaning does not rectify the problem, a more thorough cleaning of the interior of the unit may be required.
The outer housing of the unit may be removed according to the manufacturer’s instructions, once the unit has been unplugged and grounded. Accumulated dust on the fans and motors lowers air conditioning performance. Thoroughly cleaning these units may remedy the heating problem. Clearing out obstructed drain ports for the condensate is also recommended.
If cleaning out the unit does not remedy the heating problem, the problem may be electrical, arising from the compromised performance of the thermostat, fan or compressor units. These components may require attention from a specialist, which can be obtained at department stores such as Home Depot or through the air conditioning manufacturer’s support number, usually printed in the manual.