Does an Air Conditioner Need a Filter?

Air conditioners will work without filters, but only for a while. Proper maintenance includes regularly cleaning washable filters and replacing disposable filters. A clean filter improves air quality by removing allergenic particles and protects the air conditioning system from damage. Without a filter in place, dirt from the circulating air will collect on the coils and interfere with heat transfer, causing the compressor to work harder than necessary. This will contribute to the early breakdown of the machine.

Does an Air Conditioner Need a Filter?

Operating Principles

Air conditioners use a two-stage sealed coolant system to cool room air and radiate waste heat to the outside. A compressor pumps pressurized coolant into the evaporator coils located outside the room. Compression of the coolant creates waste heat which is radiated externally through the evaporator coils. On the inside of the room, the condenser coils allow returning coolant to reform as liquid, which causes the condenser coils to drop in temperature. A fan pulls room air through the filter and over the cold half of the system, returning cold air to the room.

Air Quality

One important reason for including the air conditioner's filter is indoor air quality. Many people have allergic responses to indoor pollutants such as mold spores, dust and smoke. With or without the cooling system in operation, the circulating fan will pull dirty air in through the filter and return cleaner air to the room. The efficiency of this process depends upon the quality of the air filter itself. Filters are rated on a scale of one to 12. Higher rating numbers mean the filter will remove a greater percentage of pollutant particles from the air. More efficient filters are able to remove smaller particles.

System Performance

Clogged air filters reduce air flow into the air conditioning unit and slow the movement of air across the condenser coils. The machine must work longer to produce the results set by the thermostat. More stress is placed on both the fan and the compressor, potentially reducing the life of the air conditioner. A poorly functioning filter results in higher energy consumption and higher utility bills.

Protecting Coils

Although the air conditioner's performance can be temporarily improved by simply removing a clogged air filter, damage will eventually result. Dirt the filter should have removed will collect on the condenser coils, preventing direct contact with the airflow. The dirt layer will act as an insulator and prevent air from being cooled. To compensate, thermostat settings will be set lower and the machine will again be overworked.


Cleaning or replacing an air conditioning filter is routine. Follow the manufacturer's replacement directions--the manual will specify length of use. Be sure the filter is the correct one for your model. Filters usually are marked clearly to indicate which surface faces outward. Never try to clean a disposable filter--replace it with a new one. If the filter is washable, make sure it's completely dry before operating the system.