An air conditioner filter removes dust and debris from the air entering the unit before cooling and releasing it. In order to do this, warm air must flow over the AC’s condenser coils.

There are two big consequences to not changing your filter often enough, Siegel adds: It reduces air flow, which hurts the device’s efficiency and ability to provide comfort.

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Clean the filter and replace it periodically. My dad always said changing the oil is the life of a car—same can be said for changing the filter on your window AC unit.

How often to clean an air conditioner Kelsey Hei, filtration and indoor air quality specialist at 3M, recommends cleaning an air-conditioning system thoroughly once a year.