How To Remove That Bad Mildew Smell From a Window Air Conditioner

Many homeowners take advantage of window air conditioners to save money on electric bills, cool zones of their homes that the central air unit just doesn’t cool well enough or just like to be able to really cool off a room to the point where they need a blanket to sleep at night.

A window air conditioner can be useful for all the reasons listed above, but when dust, water and heat are combined, they provide a perfect environment for mold and mildew growth if no annual maintenance is performed.

Why does that bad mildew smell appear after the window unit has been running for a few months? Window air conditioners have a drip tray that is a necessary component of the system. This small collection of water, along with heat and dust allow for some pretty nasty “muck” to collect over time. The smell associated with this “muck” is best described as being sour, moldy or a mildew smell.

The steps outlined below are the steps some homeowners take to remove the smell, but it’s always best to refer to any literature that came with the window air conditioner at time of purchase. Most window units are pressurized systems and also have a charged capacitor that could cause a shock, so at no time should a homeowner remove anything other than the case, which exposes the internal components of the window air unit. Doing anything other than removing the case may result in personal injury.

1. On smaller window air conditioners, remove the outer metal case of the unit. This should expose the coils, fan and compressor. In a larger window unit, after the front plastic and a few screws are removed, the air conditioner will slide out of the case toward the inside of the room. Be careful not to damage the metal fins on the front and rear of the unit. These are made from aluminum and will bend easily.

2. Choose a location where a hose can be used outside, such as a driveway. Place the window air conditioner on something secure such as a couple of saw horses or a secure table of some kind. The table or saw horses will be exposed to water and bleach, so choose something appropriate for this task. For larger air conditioners, an assistant may be required to lift the unit.

3. Blow the unit off with compressed air from a far enough distance to remove dust and debris, but be careful not to damage any components or blow too hard on the aluminum fins. Wipe off any surface dust or debris with a damp cloth.

4. Using a soft brush such as the type used to remove lint from a dryer vent, stroke the fins up and down to remove debris caked on to the front and rear of the air conditioning unit.

5. Fill a spray bottle approximately ¼ full of bleach and fill the rest with water. Spray directly into the area where the cool air blows out of the air conditioner. Saturate this area. Be sure to get plenty of the water/bleach solution into the blower fan while turning it slowly. Once the bottle is empty, refill with water spray in the same area. The goal here is to clean the area with bleach and water, then flush the bleach out with just water.

6. Using a hose, flush all the “muck” and debris out of the drip tray. Do not spray in the tray. The goal here is to use enough water to flush out the debris, but not to use much pressure. Pressurized water will damage the window air conditioner components. Flushing for several minutes is usually enough to sufficiently clean things up.

7. Allow the window air unit to dry for a few hours. Inspect the unit closely for any damage or debris. Dap up any remaining drops of water with a dry cloth and wipe down any surfaces that still need cleaning.

8. Reassemble the case in the reverse order or slide unit back into the case that it was removed from.

9. This should be enough to remove the smell from the window air conditioner. These steps should be taken at the end or beginning of every warm season. The window unit should be stored in a clean dry location over the cool fall and winter months.