3 Signs Your Air Conditioner Has Mold

Female HVAC technician holding dirty AC filter

The only furry, colorful life-form you want living in your home is your pet. That other fuzzy, yellow, green, pink, black, or brown stuff you see growing around your air vents? That’s most likely mold in your AC. Besides visible confirmation, other signs your air conditioner has mold include a musty smell and sudden respiratory issues. Here’s what to do about it.

But First, How Does Mold Even Get Into an AC Unit?

air conditioner cooling in a room
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To cool your home, your air conditioning system draws in warm air, cools it over the evaporator coils, blows the cooled air through the supply vents, and sends the resulting condensation to the drain pan, ultimately releasing that condensation outside via the drain line. But, for example, if either of those latter two components get blocked and cause a moisture buildup, that can encourage the formation of mold.

Leaky air vents, dirty air filters, high humidity levels in your air ducts, and air conditioning units that haven’t been used in a while (typically, regular air flow keeps mold spores from sticking to any part of the system), can contribute to mold growth, too.

So, how do you know if your air conditioner has mold? That’s actually the perfect segue to the next part.

3 Signs Your Air Conditioner Has Mold

1. You Notice a Musty Smell

Girl holding her nose because of AC smell
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One of the most common, initial signs of mold growth is a musty odor coming from your vents. Usually caused by mildew that’s most likely thriving in or near a full drain pan or HVAC system leak, this stale scent not only disrupts your indoor air quality but can also bring about a range of respiratory issues, which brings us to our next point.

2. You’re Experiencing Health Problems

Sick Couple Having Cold From Air Conditioner
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Signs of mold exposure might also clue you in to a problem, like if you or anyone else in your home start exhibiting sudden respiratory issues or allergic reactions. A few symptoms to look out for include:

  • Shortness of breath
  • Rashes
  • Sneezing
  • Itchy eyes
  • Seemingly never-ending colds
  • Asthma
  • Wheezing
  • Congestion

3. There’s Visible Mold Growth

Ceiling mold close to air duct
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Another telltale sign there’s a presence of mold? Actually seeing it with your own eyes. While obvious, visible mold isn’t always easy to spot right away, since it can be hidden inside various components of the AC unit itself. But, you may notice an infestation of mold spores hanging out around air vents or growing on the exterior of the unit.

Mold can come in all sorts of colors — from black to pink to purple to brown to yellow to green. While not all black-colored types of mold are the black mold (aka stachybotrys chartarum), if breathed in, they may still cause adverse effects, such as lung disease, allergic reactions, asthma, or even structural damage to your home. 

What to Do if You Suspect Mold in Your Air Conditioning

If any of the above sounds familiar, and you think mold in your AC might be the issue, the first thing you should do is switch off the air conditioner — in case there truly is a mold problem, you definitely don’t want to make things worse by continuing to distribute mold spores all over your home. Immediately after turning the air off, call an HVAC pro to come out and perform a thorough inspection. If mold is indeed present, you’ll need to hire a mold removal specialist right away.

You can do a quick inspection of a window air conditioning unit yourself by removing the air filter and checking the coils and other interior parts to see if they’re moldy. Suspicions confirmed? Call in a professional or clean it yourself (if it’s just a small amount).

How to Remove Mold From Your Air Conditioning

Before getting started, gather the following supplies:

  • Bleach
  • Face mask
  • Safety goggles
  • Bucket
  • Screw driver
  • Water
  • Dish soap
  • Scrub brush/sponge
  • Wet/dry vac
  • Gloves

While a mold infestation in your central air system and/or ductwork should only be handled by a mold removal specialist, homeowners can clean mold that exists in small amounts inside a window air conditioner or other portable ac unit, as those can be broken down and carried outside to prevent further spread of mold spores during the disinfection process. Here’s how to clean these types of units:

Step 1: Gear up with the face mask, goggles, and gloves.

Step 2: Turn off and disassemble the unit; carry it outside.

Step 3: Replace disposable filter or clean washable filter by soaking it in 10 parts water and one part bleach for several minutes.

Step 4: Vacuum the inside of the unit.

Step 5: Use dish detergent to clean small spots of mold inside unit and on outside cover.

Step 6. Reassemble when dry and bring back inside.

Again, if there’s a major mold infestation in your central air system, you’ll need the help of a mold remediation specialist (HVAC technicians are not experts in mold removal). These specialists are adept at containing the situation, using professional-grade chemicals to kill off the mold, and preventing a recurrence. Still, if the infestation is so overwhelming no amount of cleaning can get rid of it all or guarantee it won’t come back, you may need to replace the entire thing.

How to Prevent Mold in Your Air Conditioning

To prevent mold growth, and its associated health problems, from starting in the first place, always keep up with routine HVAC maintenance. Beyond that, be sure to:

  • Use a dehumidifier
  • Replace air filters quarterly (or wash reusable ones)
  • Keep the AC running, so airflow ensures mold spores can’t stick (raise your thermostat so the AC isn’t always running, but will kick on periodically)

FAQ About Mold in Your Air Conditioner Unit

How often should you clean your air conditioning unit?

Experts recommend a routine inspection and cleaning of your central air conditioning once or twice a year. During these appointments, an HVAC technician will be able to identify any problems (including mold growth) and suggest next steps to remedy them. 

Portable and window air conditioners should also be cleaned annually. For both AC systems, cleaning involves washing the coils, replacing (or washing) air filters, vacuuming the inside components, and wiping down the exterior, among other things.

Is it safe to use an air conditioner that has mold in it?

Absolutely not. As mentioned previously, mold can be hazardous to your health if you breathe it in, especially over long periods of time. By continuing to operate an AC that has mold in it, you’re allowing mold spores to travel throughout your living spaces — and your lungs.

What is the best temperature to run your AC for mold prevention?

It’s recommended that you maintain an inside temperature of 78 degrees Fahrenheit or lower. This helps your AC dehumidify your home, so mold doesn’t have the hot, humid environment it needs to thrive. 

You can make sure your home’s humidity levels are where they should be for mold prevention with a smart thermostat. As a general rule, your home’s humidity levels should not exceed 50% and not dip below 30%.

When to Hire a Professional

If you really, really want to DIY mold cleaning, only attempt it with a small amount of mold in a window air conditioner or other portable AC unit while wearing the appropriate safety gear. Generally, though, for serious HVAC issues like mold that can negatively affect your health, it’s best to first confirm the presence of mold with the help of an HVAC pro near you. Then, hire a mold remediation specialist to eradicate the fungi. You’ll breathe easy once again knowing you have safe harbor from the hot sun and from dangerous contaminants.

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Andréa Butler

Andréa Butler is a writer and editor. And while she hasn't been blessed with DIY skills herself, she is adept at writing and enjoys sharing home improvement tips and pool care guides for the true DIYers out there.