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How to Clean a Window Air Conditioner

Stay cool and save money with five simple tasks–most done just once a year–that ensure your unit keeps working efficiently.

Window Air Conditioner at peak of home. iStock

Window air conditioning units may not require a technician's attention, but that doesn't mean they're maintenance-free. A little TLC will help ensure that your unit performs efficiently, which can translate to savings on your monthly utility bill and a longer life for the appliance.

How to Keep a Window Air Conditioner Unit Clean

While filters require regular upkeep, the rest of these tasks only need to be done once a year.

Step 1: Wash the filter

A clean filter ensures that an adequate amount of room air will circulate over the evaporator coil, keeping it from freezing up. Never cleaned your filter? Take it out; soak it in warm, soapy water; then rinse off the crud. When your AC is on active duty, clean it monthly.

Step 2: Clean the fins

A window air conditioner has two sets of coils, the evaporator coil in the front—the room side—and the condenser coil in the back, facing outside. Their purpose is to transfer heat from inside the room to the outdoors, so the coils are covered with delicate aluminum fins. These capture and release heat more efficiently than the coils alone.

Over time, the fins on both the front and back coils will get covered with dirt, which can become a breeding ground for mold. To clean the fins (and the rest of the unit's innards), take the unit off the windowsill or out of the wall, and take it outside. Remove the screws from the housing and put them aside in a safe place. Mix some water and a few drops of dish detergent—Dawn is a good choice—in a spray bottle. Spray this solution on the fins, front and back, and let it sit for a few minutes before gently loosening the dirt with a soft-bristle brush. Move the brush in line with the fins.

The fins on the front coil are usually the dirtiest, and you'll probably see a dramatic change in their color as the dirt washes away. Rinse the fins by using a hose to gently spray water from the inside out.

More: How to Select a Portable Air Conditioner

Step 3: Straighten bent fins

Thin, delicate fins efficiently handle heat so long as they stay in place. But if fins are bent and touching each other, the unit's efficiency suffers and the cost of operating it goes up. Bent fins are a common problem on the back coil, where it's easy to brush against them inadvertently.

You can straighten them with a tool called a fin comb. It's fitted with teeth sized to match the spacing of your air conditioner's fins, allowing it to separate multiple fins with each pass. In a pinch (and with a little extra patience), you can use an expired credit card to separate one fin at a time.

Whether you use a comb or a card, the idea is to insert the object into a gap where fins are not bent, then run it down the gap until you pass through the bent section. It may take multiple passes to get the bent fins back to their original position, but it's important to get them to properly function.

Step 4: Wash the fans and the pan

Window AC units have two fans: a "squirrel-cage" blower near the evaporator and a bladed fan near the condenser. Both accumulate dirt, which can be cleaned with the same detergent solution used for the fins. Scrub the dirt off the fan and all the surrounding surfaces, then rinse with the hose. (The electrical parts of the unit are sealed and won't be damaged by the water.)

The drain pan collects condensate that drips off the coils. If its hole is stopped up, condensate can back up into the house. Sluice out the dirty water from the drain pan at the bottom of the unit and make sure the drain hole isn't plugged with debris. Remount the housing, taking care not to touch the fins, then refasten with the screws.

Step 5: Store it in the off-season

Although it may be tempting to leave the heavy unit on its windowsill year-round, your AC will last longer and perform better if you take it out and store it through the cold months. Park the unit in a dry, indoor space with a cover to keep out dust.