Covering window air conditioners during winter

Consumer Reports News: September 11, 2007 05:40 PM

I just moved to a place with cold, snowy winters. I’m considering leaving a very heavy second-floor air conditioner in the window year-round. Is this a good idea?—John W., Montpelier, Vermont

We recommend you remove any air conditioner from a window location. During the winter months, heat could escape through the accordion extension panels on the A/C and the chassis; cold air could also infiltrate your home the same way.

To avoid injury, move the unit with another person. Once you’ve removed the air conditioner from the window, drain any water inside it, clear off debris, and wipe the internal surfaces clean. Be sure to store it in a dry spot in an upright position. You could end up damaging the compressor if you store an A/C on its side or upside down and, next cooling season, attempt to operate it without allowing the lubricant to flow back to the compressor.

If you decide to leave your air conditioner in the window, follow the manufacturer's instructions for wintertime storage. If the manufacturer suggests covering the outside of an air conditioner, be sure not to trap any water in it--mold could grow inside it. To dry the interior, run the fan-only mode for several hours over the course of a few days when the weather is dry and mild.

After the air conditioner is dry, you can prevent rainwater from entering it by protecting its exterior with a fitted cover or plastic sheeting. Some manufacturers recommend leaving the exterior uncovered so that moisture can evaporate with natural airflow.

Inside your home, seal gaps where the unit and extension panels meet the interior frame and window sash with weather stripping; also seal around and behind the inside grille if needed. If there’s still a draft, cover the inside grille.

Air conditioners that are permanently mounted through a wall usually have a slide-out chassis or mounting sleeve. If possible, remove and store the chassis as directed above. Mounting sleeves often have a block-off plate that seals the area once you’ve removed chassis. If there’s not a mounting sleeve, seal the area using plywood, weather stripping, and insulation.

Essential information: To cover air conditioners that are not at ground level, you’ll need a sturdy ladder. Read our report on ladders and use our Ratings to find the best model. And whenever you use the ladder,  follow our safety advice.

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