How To Clean Mold From Your AC (Window and Portable)

Mold is a fungus. It grows mainly in moist environments, indoor or outdoor, in any season. It’s a hardy fungus that can eventually damage property and induce detrimental health effects in people. Black mold is famously dangerous and toxic, but any mold can cause problems.

When you discover mold, the sooner you deal with it, the better. Mold is challenging to get rid of, and the longer it has to take root in your home or office, the more it will spread. Because it spreads by releasing spores to float on air currents, land, and take root elsewhere, you are on the verge of having a severe mold issue once mold gets into your air conditioner.

Knowing how to clean a window air conditioner mold has invaded is vital to know: as long as mold is in your AC unit, that unit is actively assisting the mold in its quest to spread out everywhere.

What Causes Mold In Air Conditioners?

Because mold spores travel on air currents, they’re pretty much everywhere. You’ll never be completely rid of them. You can only make it harder for mold to take root. The things it needs to thrive are what every living thing needs: water and something to eat.

Because your air conditioner’s condenser unit sheds water, the interior is a good host location. Since enough dust can act as a food source, the dusty, wet insides of your air conditioner can be a mold paradise.

Where Can You Find Mold Hiding In AC Units?

Many moving parts make up your AC unit, so it follows that there are many places where mold might be able to take hold and grow. Because mold can grow quickly (taking hold in as little as 24 hours), you have to be sure to get as much of it as you can out of your AC unit. If you clean all the mold from your flex ducts but neglect the air vents, you’ve only paved the way for mold to spread again.

Supply Plenum

The supply plenum is the hub of your air conditioner unit. Cool air moves into this box-like structure before it gets routed elsewhere. Mold tends to grow here because, as a hub-like area, air collected here has been bouncing around over many of the AC unit’s other parts, and that air will be rife with mold spores if there are any in the unit.

Air Vents

Mold can collect on or near the AC unit’s air vents because this is the spot where the cooled, conditioned air meets the warmer, as-yet-untreated air just outside the unit. This can cause condensation, which in turn provides the moisture mold needs to survive and spread.

Flex Ducts

If your air conditioner has flex ducts, they are as susceptible to mold growth as any other part. However, they are more vulnerable to mold re-appearing there because ducts’ flexibility comes from the corrugated nature of their walls. This means there are orders of magnitude more nooks and crannies for mold to hide in, even when you clean it.

Trunk Line

Your AC’s trunk line comes from the supply plenum and pushes air through more ducts and vents. Since the supply plenum is prone to getting mold building up in it, it follows that as the air flows into the trunk line, that trunk line will get a dose of as many mold spores as the plenum has in it. Given moisture and dust or other organic matter like skin cells, mold grows well.

AC Styrofoam

Styrofoam acts as insulation in your AC unit. It makes sense that mold can easily build up: foam can harbor moisture from condensation resulting from the temperature differences between the two sides of the insulation.

What Mold Looks Like

Noticeable Sign of Molds In Air Conditioner

You may not immediately recognize that mold spores are growing in your window air conditioner unit. But there’s an order in which the mold makes itself known, so coming across any of these symptoms means you need to take some action.

Allergy-Like Symptoms and Sickness

Before you ever see mold build-up in or on your air conditioner unit, it can still be there, growing, multiplying, and sending spores out into your home. That means you may experience symptoms of mold exposure before you see any mold. These can include:

  • Breathing difficulties
  • Cough
  • Eye irritation
  • Headaches
  • Sinus congestion
  • Throat irritation
  • Wheezing
Musty Odors

Even if you don’t experience allergic reaction-style symptoms, you might also detect some odors. Moldy smells are fairly definitive indicators, but so are musty smells. It’s fair to say that if any kind of unpleasant odor issue comes from your AC unit, it needs to be checked out.

Visible Mold Growing

Once you can see the mold on your AC’s vents, styrofoam, or anywhere else, you’ve got a sizable build-up and need to act immediately. Mold spores are invisible to the naked eye. Once there are enough of them gathered together for you to see them, that’s a lot of mold.

Molds at Home

How To Clean Mold from a Window AC

You’ve found the mold, so you need to get rid of it. Once you have a plan and the right materials, it’s not a complicated process. The materials you need include:

  • Rubber gloves and eye protection
  • Bucket
  • Bleach
  • Hot water
  • Brushes and/or scrubber sponges
  • Screwdriver

After gathering these materials, you’ll only need to follow these steps:

  1. Unplug the AC unit.
  2. Remove the unit from the window (this is why you needed the screwdriver).
  3. Be careful not to get water on the unit’s controls or near where the power cord connects; other than that, the unit can withstand water.
  4. Take out the air filter and (depending on the filter) replace or clean it (hot water and dish soap).
  5. Open the unit’s metal cover with the screwdriver.
  6. Vacuum the interior to remove visible dust and debris.
  7. Using a mixture of about a half-cup of bleach per three gallons of hot water, scrub the insides of your AC unit with brushes or sponges. You may need to repeat this step, rinsing with water in between.
  8. Be sure to scrub all the spots you can because it will just grow back if any mold escapes your efforts.
  9. Allow the unit to dry for 24 hours. Failure to do so might end up giving mold a new water supply so it can grow back.

How To Clean Mold from a Portable AC

Portable ACs are much smaller than window units, and disassembling one very well may void your warranty. Still, the steps for cleaning it are very similar, though you may want to skip taking it apart.

  1. Unplug the unit.
  2. Remove and replace the air filter.
  3. Using your vacuum cleaner’s crevice tool, vacuum out as much of the unit as you can.
  4. With a bleach-water mixture, wipe down the unit, paying particular attention to the vents and anywhere you see visible mold.
  5. Allow the unit to dry for 24 hours.

Health Risks If Molds Are Not Removed

As outlined above, allergy-like symptoms can arise when mold gets sprayed out of your unit and into your home. While mold doesn’t always affect everyone, it’s never good to breathe the spores.

People with asthma or other respiratory issues will be more likely to suffer the symptoms listed above. Extended exposure to mold can induce memory loss, lethargy, and even fever, so mold removal must be done immediately upon discovery.

Helpful Tips To Prevent Mold Growing In AC

The best way to clean mold from your AC unit is to prevent it from growing there in the first place. Preventing mold in your AC involves actions you should take to prevent mold from your entire home:

  • Keep your AC unit clean.
    Since mold can use the skin cells in dust as a food source, clean your unit regularly so you can prevent dust build-up. If mold doesn’t have food, it won’t grow.
  • Make sure the AC drains run properly.
    Your AC unit produces condensation, and if it can’t get out of the air conditioner, that moisture will engender a lovely environment for mold.
  • Regularly run the unit on its fan mode.
    This allows air to circulate without generating condensation that collects when the compressor is in use, which helps dry the interior.
  • Use a cover.
    Once cooler weather comes around, and your AC unit will be beaded into hibernation mode, cover it to keep out moisture, leaves, or other contaminants.
Anti Mold Spray Bottles

People Also Ask (FAQ)

No matter how comprehensive a guide we have, people will still have unanswered questions. To that end, here are some answers to the more common inquiries.

Is the black stuff in my AC mold?

Probably so. It might be dirt, mud, or even animal droppings, but it’s probably mold. Even if it’s one of those other things, it still needs to be cleaned out. Following the steps listed above for cleaning mold will work just as well if that black stuff is one of those other things.

Does vinegar kill mold in air conditioners?

It does, but undiluted, it can be potentially damaging to your air conditioner’s parts. The upside is that any lingering vinegar fumes will not act as irritants to your eyes and mucus membranes, as bleach might.

What kills mold instantly?

Bleach. We’ve all seen it makes holes in the color of our shirts when we accidentally splash it. It does the same to mold, though using it undiluted is not recommended. Also, it’s overkill, as a water-bleach mixture will do the job.


Mold can be dangerous. At best, it can be a nuisance, but since it can cause health problems, you should deal with any mold you find as soon as you can. Air conditioners are especially problematic since they blow air through your home, and if there’s mold inside the unit, it will blow out onto you and your family.

Keeping your portable or window AC unit clean helps keep mold from growing in or on it. If the mold has taken root, though, cleaning it up is relatively painless. It requires some soap, bleach, and a little elbow grease. The reward for your efforts will be clean air, for you and your family to breathe.

Josh Mitchell

Josh Mitchell

My name is Josh and I am obsessed with DIY and improving my family home. HVAC topics can be tricky for homeowners so I decided to share my knowledge on the subject. When I am not working on DIY projects, you can find me at the beach or my local coffee shop.