An air filter is located above the evaporator coil in an air conditioner, typically in a special slot within the duct system or inside the return grille. The air filter is made of paper and is either folded fuzzy-looking.
When owners do not change the air filters in their air conditioners regularly, air flow begins to decrease. The air filter helps the air-conditioning unit to run more efficiently. The filter cleans the air by removing particles or debris from the air stream. As the air filter functions, it collects particles. When too many particles build up on the filter, it can lead to air pollution or cause the evaporator coil to fail. When this occurs, the unit can not blow cool air and the system begins to perform poorly.