How to Clean a Window Air Conditioner (Filter, Coils & Drain)
A window AC that blows weak, warm, or musty air is usually just dirty. Cleaning the filter and coils once a season restores cooling, kills the smell, and cuts energy use. Plan about 30-60 minutes.
Unplug and Pull the Filter
Always unplug the unit first. Pop off the front grille (it usually snaps or unscrews) and remove the foam or mesh filter. Wash it in warm soapy water, rinse, and let it dry fully before reinstalling — a wet filter grows mold. If the foam is crumbling, replace it. A clogged filter is the #1 cause of weak cooling, so check it monthly in summer.
Clean the Coils and Fins
Behind the filter are the evaporator coils (front) and, at the back, the condenser coils. Vacuum loose dust with a brush attachment, then spray a no-rinse foaming coil cleaner on the coils and let it drain out the back per the can. Straighten any bent aluminum fins gently with a fin comb so air flows freely. Dirty coils are the second-biggest reason a window unit can't keep up.
Clear the Drain and Kill the Musty Smell
Window units drain condensate out the back; algae and dust can clog the channel and pan, causing a musty smell and water dripping inside. Wipe the pan, clear the small drain hole/channel with a pipe cleaner, and wipe surfaces with a vinegar-water solution to kill mold. Let everything dry, reinstall the filter and grille, and you're done. Repeat the filter clean monthly and the full clean once a season.
Parts & Tools
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FAQ
Almost always a dirty filter or dirty coils. Clean the filter monthly and the coils each season. If it's still warm after cleaning, the unit may be low on refrigerant or undersized for the room.
Mold and algae in the filter, coils, and drain pan. Wash the filter, wipe the coils and pan with a vinegar-water solution, and clear the drain channel. Letting parts dry fully before reassembly prevents it returning.
Rinse the filter monthly during cooling season and do a full coil-and-drain clean once a year (spring, before you start using it). Clean coils can cut energy use noticeably.
Sources
Documents this guide was checked against. How we verify.
Always unplug an appliance and shut off its water supply before servicing. This guide is informational and not a substitute for a qualified technician.