Evaporation filters are part of the evaporator and will need replacing periodically as inevitably they will slowly get clogged up with particles as air moves through. The evaporator filter essentially absorbs and vaporises heat from the air in the passenger compartment once cold refrigerant has been released into it. A blower then distributes cooler air. A secondary benefit of the evaporator is that it dehumidifies the air.
Evaporation filters for every make and model of car are available and easy to obtain once they need replacing. Show Less