Dust Accumulation

The accumulation of dust on the cooling fans and other parts of a window air conditioner may lead to mold. Mold spores travel inside dust particles and require moisture to become active. When dust remains on the air conditioning unit and reacts with the moisture expelled moisture, mold can begin to breed. Dust your window-mounted air conditioning unit weekly to minimize your risk.

Dirty Filter

Most window-mounted air conditioners contain a mesh contaminant filter intended to minimize the accumulation of bacteria and fungi such as mold. If you do not properly rinse the filter and clean it from time to time, it will lose its effectiveness. Read your manual for exact removal and cleaning instructions but in most cases you can access the filter by opening up the grill. Use vinegar or detergent to clean your filter at least once every three months.

High Relative Humidity

Mold becomes a serious threat when relative humidity exceeds 60 to 70 percent. If you use your window-mounted air conditioner regularly in humid weather, the likelihood of developing mold will remain low due to the ongoing air circulation. If you allow the air conditioner to stagnate for long periods in humid weather, you may develop mold due to the device's close proximity to the outdoors and lack of air circulation.

Failure to Fan the Air

The "Cool" setting on a window-mounted air conditioner draws out cold air by fanning moisture into a room. That same moisture may fester and cause mold if not properly filtered. After using your air conditioner, use the "Fan" or "Dry" setting to blow air through the device, evaporating the remaining moisture and promoting continued air circulation into the room. Do this for at least an hour after every air conditioner use.