How to Tune Up Your Window Air Conditioner

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How to maintain your window air conditioning unit to ensure proper and efficient operation.

Every homeowner or renter should be able to perform some routine preventive maintenance on their window or thru-wall air conditioner to ensure that it works properly and efficiently when you need it most. When air conditioners are under stress, which happens hen outside air temperatures are 90 degree F or above, they tend to fail. This article will describe some simple ways to make sure this does not happen to you.

Window Air Conditioner Components

Cleaning the Outside of the Unit

Unplug the air conditioning (AC) unit and take it outside and set it on a flat surface. With a wet cloth and household cleaner, wipe the front and sides. Next, remove the front cover and clean it thoroughly. Depending on the model, the cover is held in place with screws or tabs along the sides that can be pressed in to free the cover. Clean the louvers or flaps on the front cover that direct airflow into the room.

If necessary you can look up the AC model on the manufacturer’s website to order replacement items such as control knobs, louvers, and the baffles that extend from both sides of window-mount air conditioners.

Filter Cleaning

Almost all window AC units have washable mesh or foam filter screens. The filter is installed on a plastic frame right behind the front cover. In some models, it slides out of a slot in the front cover. It should be cleaned once a month during the cooling season. For foam filters, wash the filter under a faucet with warm water and a mild detergent. Metal or mesh filters can be rinsed under a faucet or with a hose to clean out any dirt and debris. You may need to consult the owner’s manual for specific instructions.

With any type of reusable filter it is important to let it dry completely before reinstalling it back into the window AC. If the filter has any tears or is worn out, it needs to be replaced. Check the owner's manual to find the right replacement filter. Foam filters material can be purchased at hardware stores or home centers and cut to size with scissors.

Clean Evaporator Coil

Use a vacuum with a soft-brush attachment to the aluminum fins located directly behind the filter. Be careful not to bend the fins; clean the evaporator by moving the vacuum brush in the same direction that the fins run. Bent fins block the flow of air through the unit which reduces the cooling capacity and can cause coils to freeze. Straighten any bent fins gently with a fin comb or a very small flat screwdriver.

Verify that the thermostat sensor is positioned properly in its bracket and is not touching the evaporator coils. The thermostat is a small metallic bulb on the end of a thin copper tube. Be careful not to kink the copper tubing.

Cleaning the Condensate Drain

There is a small drain that is located below the evaporator coil at the bottom of the unit. The condensate drain allows the condensation running off the evaporator coil to be removed from the condensate pan to the outside. To check that it is clear pour a cup of water slowly into the condensate pan and check that it runs out. You can clear the drain by using a soft wire or pipe cleaner to remove any blockage.

Cleaning the Condenser Coils

With a garden hose gently rinse the exterior (the coils facing the outside) coils of the unit. High water pressure with deform the fins and cause the compressor to overheat and can damage it over time. You may be able to purchase some nickel-safe coil cleaner that you can spray on the condenser coils and rinse off. Straighten any condenser coil fins with a coil comb.

Test Run

Reinstall the window unit in the opening and make sure that it is pitched down slightly so the water in the condensate drain pan runs outside. The outside edge of the unit should be at least ¼ inch below the window sill. Inspect the weather stripping between the unit and the window frame. The side baffles should securely against the window frame. Fill any gaps with foam weatherstripping for window air conditioners.

Keep any foliage at least two feet away from the unit to allow the condenser coil to have proper airflow.

Turn on the air conditioner and listen to the unit run. Any humming sounds may be caused by vibrations inside the unit. Turn off and unplug the unit and check for loose fasteners or screws that might be causing the noise. If the thermostat bulb is touching the coils, that could make a noise. Clicking noises may be the fan striking the unit's housing which can occur if the unit is not level.

Check that cold air is blowing out of the unit. It you have a thermometer place it near the discharge area of the AC for about 5 minutes. It should be around 55 degree F or less.

Helpful Tips

Window air conditioners installed in a shady spot could run up to 10 percent more efficiently, according to the U.S. Department of Energy. Seal the perimeter of the installed unit with new weather stripping. Make sure that the unit is secure so that a burglar can't push it in and or that it can’t fall out of the window and injure someone.

If you happen to shut off the unit you should wait at least 10 minutes before restarting it. This allows the pressure in the refrigeration system to equalize and will prolong the life of your air conditioner.

Window air conditioning units are not typically serviced by do it yourselfers. Covers need to be removed to access the blower and condenser fans. If you have any problems with the unit not running, the compressor shutting off continuously, or the unit not keeping the space cool, you should call a qualified appliance repair technician.

Additional Information

Association of Home Appliance Manufacturers (AHAM)

Energy Star


Robert Guida
Posted on Jun 1, 2011
Roberta Baxter
Posted on May 29, 2011