If I had a nickel for every call when I have asked a customer, “Is your filter clean?,” I would have a lot of nickels. If you don’t change your filter on a regular basis (depending on the filter), it will no longer be able to filter air properly, letting dust and contaminants get into the AC. Dust jams the moving parts of an AC, such as fan motors and valves, and the filter becomes less energy-efficient. There are several factors that determine how often your filter should be changed: The type of filter, overall air quality, pets in the home, number of people living in the home, and level of pollution and construction around your home.