an air conditioning unit in a window, viewed from exterior

Window Air Conditioner: How to Fix It, Clean It, and Make it Like New

As the heat of summer is bearing down, millions of window-mounted air conditioners are getting a real workout. That means many owners of said units wonder why their air conditioners aren’t working properly.

an air conditioning unit in a window, viewed from exterior

In most situations, consumers can fix a window air conditioner, provided they have the right information and a fairly inexpensive tool. If you have a window air conditioner in your home, here’s what you need to know to fix it, clean it and make it like new.

An easy DIY project

Window-type air conditioning units are the most often neglected than any other household appliance. This is a pity because they can be big energy users. A little maintenance means homeowners can save money on utility and repair bills.

With the right information and access to replacement parts, you should be able to repair a window air conditioner yourself, saving the cost of a service call or replacing the unit altogether.

Basically the same

All residential window air conditioners have a cooling system consisting of four primary components: a compressor, an evaporator, a temperature-sensing device, and a condenser.

Air conditioner cooling systems are better understood if you think of them more as a device that removes heat and humidity from the air than a device that cools the air.

These are the essential maintenance steps you should take to keep your window-mounted air conditioning unit operating in tip-top condition while using the least amount of energy:


Once each month during the heavy-use season, replace (or clean) the filter located in the front grill—the cost to replace: About $20.


The condensing coils on an air conditioner get very dirty, and the dirt accumulates inside the coils, out of sight. Once a year, remove the entire cover of the air conditioner to gain access to the coils and then clean them by blowing compressed or “canned air” on them. Falcon Dust-Ofworks well.

Here are solutions for the top four repair dilemmas with window air conditioners:

1. Bent fins

Don’t despair if you’ve accidentally bent the delicate aluminum fins on the rear of the unit. They need to be straight for the best operation. This is not as tedious as it might appear. will send you a handy fin-straightening comb. Cost about $16.

2. A motor is running, but no air is blowing

Air conditioners have two motors: the compressor and the fan motor. Only one may be running. If, after removing the cover of the unit, you discover the fan blade is very stiff and difficult to rotate, the fan motor may need oiling or replacement.

3. Water leaks from the front of the unit

This is normal. All air conditioners should tilt slightly backward to allow for proper removal of condensed water that accumulates.

4. The air smells musty

Air conditioners remove moisture from the air. Most of it is evaporated from the unit. However, some water can stagnate in the base of the air conditioner. Also, dirt, lint, or dust can collect in the water pan at the unit’s base and absorb water, allowing mold and mildew to grow. All this leads to bad smells. Thoroughly clean the water pan each year when you clean the condenser coils.

Get help

Need more help with your window-mounted air conditioners? Check, where you can live chat with a repair technician, plus get the exact parts you may need. Super helpful site!


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8 replies
    • Max says:

      Follow the suggestions in this article, but if you’ve cleaned the coils and filter and you still get just hot air, sadly, that is the most common reason people replace a window a/c unit. If the fan is still running and you just get hot air, there’s a good chance that the refrigerant has leaked out or the compressor has failed. If it’s a relatively modern unit with an electronic front panel control, that is also something you cannot fix yourself unless you are handy with basic wiring, maybe soldering, and can foot the bill to replace the entire control module because those modules are virtually always “replace the whole module” parts. All of these cases are going to run into the hundreds, not dozens, of dollars, making the unit not worth repairing.

  1. missy says:

    Dear Mary,

    Please tell your fans to be SURE to lock the window somehow after they have
    installed the AC.

    Especially if the AC is in a window with access nearby (like the roof in your
    photo), it can be easily removed and your house can be entered while you are
    home, asleep or gone. (It has happened to me.)

    Please show people how to use a bar (inside) to jam the window closed hard
    onto the AC.

    OR, some manufacturers recommend drilling a hole through both parts of the
    window sash and wedging a bolt in so the window cannot be opened (and the AC
    removed to the side roof–from the outside–which leaves the window fully opened).

    A window AC window needs to be extra secured because they are so Visible and
    Vulnerable. This is important. Don’t wait even ONE day. Thanks, Mary.

  2. Gehugh says:

    Great reminders! Here’s one more…
    If your window unit is exposed to the elements during the winter, it probably has been wrapped in an insulating blanket, a tarp or even a plastic garbage bag. Be sure to remove winterizing wraps before preparing your unit for summer use. I can still see the horrified look on a friend’s face when, after she had suffered a week of 100°+ temps in her apartment, I removed the plastic wrap from the AC unit and all was well after that. LeukemiaThe landlord had not gotten around to removing it!

  3. Linda Carlis says:

    Mary, thanks to you I always have sniper on hand. I use it to spray down the inside and outside parts of the window a/c unit once a month when I clean the filter. It makes it smell fresh and keeps down the mold and mildew as this unit is in the shade. I leave it off until it is dry and clean the unit once a year. Here in Southeast Florida we use air conditioning all year, nearly every day.


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