Solved! What to Do About Mold in the Air Conditioner (2024)

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Determine the extent of mold growth in your AC and take the proper steps to remove the health hazard.

By Glenda Taylor and Bob Vila | Updated Jun 23, 2023 6:17 PM

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  • Solved! What to Do About Mold in the Air Conditioner (1)

Solved! What to Do About Mold in the Air Conditioner (5)


Q: There’s been a mysterious, slightly moldy smell in my home all summer, and this morning, when our window air conditioner kicked on, I noticed that the odor unmistakably came from the unit. I know it’s unhealthy to breathe air that contains mold spores but I’d rather not buy a new AC if I can remedy the problem myself. Is there any way to remove mold from an air conditioner?

A: Molddoes have a tendency to grow inside air conditioners that sit unused for a while. It’s likely that mold developed in the unit over the winter and you didn’t notice it until you turned on your AC unit this summer. And you’re rightto be concerned about the health issues this can cause: Mold spores produce allergens that can lead to sore throats, headaches, and various respiratory symptoms. While odds are the mold in your AC unit is not the scary black mold (Stachybotrys chartarum) that you’ve heard about, inhaling mold spores of any type can result in respiratory disorders.

RELATED: 14 Surprising Places Where Mold Hides in the Home

Successfully banishing mold from an AC depends on where it’s located. If the mold is accessible, you may well be able to remove it; but if it’s growing in an area that’s difficult to access, you’ll probably have to replace the unit. Read on for the sleuthing tips and cleaning steps you need to bring clean, safe, cool air into your home again.

Turn off your air conditioner to prevent further mold spores from entering your home.

If you suspect that mold is in your AC unit, the US Environmental Protection Agency recommends turning it off so no more mold spores can circulate and contaminate your home.

Inspect the unit to determine the extent of the problem.

Unplug the unit, remove the front grille cover (most snap off but some are held in place by screws), and then pull out the filter beneath the grill. Grab a flashlight and inspect the inside of the unit for the signs of mold growth, which may appear as streaks or clusters of brown, black, or greenish stains, some of which may appear fuzzy. Mildew, a common type of mold, produces powdery gray or white stains. If you find just a few traces of mold on the hard surfaces inside the unit, proceed with cleaning. If it’s filled with heavy mold growth, indicated by mold and mildew deposits that cover one-third or more of the surface area of the case and the internal workings, it’s probably time to replace the unit (see below for the problems associated with heavy mold growth).

Solved! What to Do About Mold in the Air Conditioner (6)


Clean small amounts of mold from inside the cabinet and/or the grille.

AC units vary in the way they are assembled, so check your owner’s manual to determine how to identify and disassemble the exterior cabinet so that you can access the interior. Before you start, assemble your tools and materials and then don a dust mask, goggles, and gloves.

MATERIALS AND TOOLS Available on Amazon
Wet/dry vacuum with a nozzle attachment
Commercial AC coil cleaner
Garden hose
Dish soap
Large plastic bucket
Scrubbing sponge

  1. Remove the unit from the window, using a screwdriver to remove the frame that secures it. AC units are heavy, so recruit someone to help you take it to your yard or driveway and place it on a concrete surface or on a large piece of plywood.
  2. Remove the grille and the filter from the front of the unit. Soak the filter soak in a sink with hot soapy water to which you’ve added approximately 1/2 cup of bleach.
  3. Remove the top and the back of the cabinet, following the directions in your owner’s manual.
  4. Vacuum out dust and debris from the inside of the air conditioner. Use a nozzle attachment to get out as much as possible.
  5. Spray the coils (U-shaped metal tubes near the front and the back of the unit) with commercial coil cleaner and let the product dwell as directed by the manufacturer to dissolve anything that’s collected on AC coils. Cleaning the gunk on the coils is crucial because it provides a breeding ground for mold.
  6. Spray the coils with a garden hose to remove the coil cleaner solution. It will have dissolved the gunk and it should spray right off. While window AC units are fairly waterproof, avoid spraying the controls and the spot where the electrical cord is attached.
  7. Fill a plastic bucket with a few gallons of hot water and about 1/2 cup of household bleach.
  8. Saturate a scrubbing sponge in the bleach solution and use it to wipe the inside surfaces of the AC unit, removing all traces of visible mold. The bleach will kill residual mold spores.
  9. Spray the filter that’s been soaking in the sink with the hose to remove all debris.
  10. Allow the unit to air-dry completely, which could take up to 24 hours, before reassembling the unit and reinstalling it in your window.

Take precautions to prevent future mold growth.

Once you’ve had mold in the air conditioner unit, there’s an increased risk that it will develop again despite your cleaning efforts. This is because mold spores could remain within the inner workings of the unit that you were unable to reach. The presence of dust in the unit helps mold spores adhere and grow, so make it a practice to remove the grille and filter every few weeks and vacuum the interior of the unit to keep dust from settling.

RELATED:The Dark, Dirty Truth About Household Mold (And How to Rid Yourself of It)

In addition, don’t shut off your AC if you won’t be using it for a few days or longer during hot weather. This is a common practice when people go on vacation, but when the weather is warm and humid, mold is more likely to get a foothold in the AC unit. The air movement that occurs when the unit is running helps prevent mold growth. If you want to save on cooling costs when you’re gone, set the thermostat on your air conditioner to a higher-than-normal temperature. For example, if you usually set the temperature to 75 degrees Fahrenheit when you’re home, set it 10 degrees warmer to 85 degrees Fahrenheit before you leave. That way, the AC will not run as often, but it will still cycle on occasionally when the temp in the house rises. This will allow air to circulate through the unit and reduce the risk of moldgrowing while you’re gone.

Replace a window AC unit that’s filled with heavy mold.

If upon your initial inspection, you discover rampant mold and mildew in the air conditioner, do not attempt to clean it. Visible heavy mold indicates that more mold is flourishing in places you cannot see or easily reach, such as within the fan motor casing. Alternately, you could call a mold remediation specialist to inspect the unit to see if it can be professionally cleaned, but the consultation could cost as much as purchasing a new air conditioner. Bottom line: It’s unhealthy to breathe air contaminated with mold spores, so if you can’t effectively clean the unit, it should be replaced.

Some jobs are better left to the pros

Get free, no-commitment estimates from mold removal experts near you.

Solved! What to Do About Mold in the Air Conditioner (7)


Solved! What to Do About Mold in the Air Conditioner (8)





Solved! What to Do About Mold in the Air Conditioner (2024)


What kills mold in air conditioner? ›

To clean mold and AC, unlock and remove the filter. If it's disposable, replace it. If it's reusable, wash it in a mix of one-part bleach to 10-parts water. Allow it to soak for at least 10 minutes to kill any mold.

Can you get rid of mold in an air conditioner? ›

You can use diluted bleach or distilled white vinegar, or you can buy an Environmental Protection Agency-registered mold removal solution from your local hardware store. Aim for a 1:3 ratio of cleaning solution and warm water. Take apart the AC unit: Use a screwdriver to remove the grille from the front of the unit.

How do you get mold out of air conditioner coils? ›

Use the brush attachment on a shop vacuum to remove the layer of dirt covering the coils. If you don't have a vacuum with a hose attachment, use a soft brush to gently brush away any dirt. Work slowly to avoid causing damage to the sensitive fins and coils. Spray alkaline coil cleaner over the fins and coils.

Why do I keep getting mold in my air conditioner? ›

The air conditioner's drain line can get clogged with leaves and other debris from the outside. This causes water to back up and leak into the AC unit, which will grow mold on its interior surfaces. To prevent this problem, AC lines should be cleaned out and drained periodically.

How do I keep my air conditioner mold free? ›

How to Prevent Mold in HVAC Systems
  1. Maintain the drain pans. ...
  2. Replace air filters regularly. ...
  3. Apply an HVAC mold inhibitor. ...
  4. Use a disinfectant. ...
  5. Keep ducts dry. ...
  6. Check the air intakes.
Jun 26, 2018

Can a moldy AC make you sick? ›

Watching for Mold

Living or working near an old and moldy air conditioner can increase your chances of respiratory infection.

Is the black stuff in my AC mold? ›

An AC unit that has sat turned off for any amount of time in warm, humid conditions may very well have developed mold and mildew. As the AC is turned on, wet, black particles may blow out of the unit. Also, be on the lookout for moldy patches on the vents, evaporator coils, or any condensation pans.

Can you spray bleach in an air conditioner? ›

Bleach and Vinegar are Corrosive to metals

The reason you shouldn't use bleach or vinegar to clean your AC drain line all boils down to the fact that these chemicals are corrosive to metals. In other words, they literally eat away at metal.

How do I get rid of black mold in my HVAC system? ›

Use an EPA-registered disinfectant labeled for HVAC use to clean non-porous surfaces (Ductwork, coils, plenums, pans, etc) of mold, mildew, and other dirt. BIOSPRAY-TOWER ready-to-use disinfectant and mold cleaner will kill and remove mold, mildew, and odor-causing bacteria.

Can you spray vinegar on AC coils? ›

Yes, vinegar mixed with water is often used to clean AC coils at home. However, vinegar is usually effective only against lighter dirt build-ups. Nevertheless, you can keep your coils in good shape by mixing white vinegar and water in a spray bottle and spraying the mixture onto the coils.

How common is mold in air conditioner? ›

Mold is a common problem in warm, moist areas that don't get a lot of light. Unfortunately, your air conditioner can turn into a prime target for mold growth if it is not properly maintained. Organic matter from airborne dust and dirt can build up in the filter, giving mold the material it needs to breed.

What is difference between mold and mildew? ›

Mold generally looks slimy or fuzzy, tends to have a raised texture, and can come in a rainbow of colors, including deep green and black. Mildew is powdery, looks white or gray, always appears flat, and grows on surfaces.

What is the best temperature to prevent mold in the air conditioner? ›

Keep the thermostat at 78 degrees or above. A higher thermostat setting and slightly warmer air temperature results in drier indoor air. In the cooling mode, temperatures lower than 78 degrees generate more humid air and cool indoor surfaces, increasing condensation that breeds mold.

Can too cold AC cause mold? ›

Some of the more common AC system related pathways contributing to mold incidence include: Cold AC supply air duct leakage into the unconditioned attic or crawl space.

Where does mold grow in AC unit? ›

Where Does Mold Grow in HVAC Systems?
  • The drain pan. Air conditioners and high-efficiency furnaces draw moisture from your indoor air. ...
  • The condensate drain line. This is a pipe that allows water to exit the drain pan and empty outdoors. ...
  • The evaporator coil. ...
  • The air ducts.
Mar 19, 2021

Is there a spray that kills mold? ›

Concrobium Mold Control is an innovative, market-leading product that effectively eliminates existing mold, prevents mold re-growth and eliminates musty odors with no harmful chemicals. The unique technology is used by homeowners, professional remodelers, contractors and remediators.


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