For central air conditioners, the filter is usually located somewhere along the length of the return air duct. Common filter locations are on walls, ceilings or the air conditioner itself. The filter of the room air conditioner is installed on the grill facing the room.
Some types of filters are reusable; others must be replaced. They come in many types and efficiencies. During the cooling season, clean or replace the filters of your air conditioning system every one or two months. If your air conditioner is heavily used, dusty, or you have furry pets in your home, you may need to pay more attention to the filter.