Mold in AC Unit: Coils, Drain Pans and Window Units

The EPA says one function of the building heating, ventilation and air conditioning (HVAC) system is to remove moisture from the air. As warm air crosses the cold evaporator coil, water condenses on it, drips into a pan, and drains away. Every part of that path can grow mold:

• The evaporator coil. Dust sticks to a wet coil and feeds mold. University of Georgia Extension says dirty wet coils can result in mold in ductwork.
• The drain pan. The EPA says the presence of substantial standing water and/or debris indicates a problem requiring immediate attention.
• The condensate drain line. When it clogs, water backs up into the pan, the air handler or the ceiling below.
• An oversized unit. The EPA explains that a unit that is too big will cycle on and off frequently, resulting in poor moisture removal. UGA also notes that oversized A/C units do not dehumidify adequately.

Texas makes all of this harder. The state has hot summers and mild to cool winters, and NOAA reports the number of very warm nights has been increasing since the 1970s. More hours of cooling means more water through the coil and pan, and more chances for something to back up.

Signs of mold in an AC unit:

• Dark spots or fuzz on the coil, drain pan, or inside the air handler cabinet
• Black dots on the louvers or just inside the front grille of a window unit
• A musty smell when the system starts
• Water around the indoor unit, or a stained ceiling below an attic air handler

Black mold in an AC unit isn't automatically more dangerous than any other color. The CDC says you do not need to know the type of mold to deal with it, and it does not recommend routine mold testing. Mold of any color is a sign of a water problem. For more on the "black mold" question, see is black mold dangerous?

Window units are the most common place people find AC mold themselves, and the hardest to fully clean.

Consumer Reports says harmful mold often first shows up as clusters of tiny black spots on the duct just inside the louvers, which can mean more mold deeper in the unit. Its advice:

• Cleaning the louvers helps only partly. Consumer Reports calls it a good first step, but only a partial solution.
• Check every season. Look for visible mold when you put the unit in. If mold is deep in the unit, the owner must either have it professionally cleaned or buy a new unit.
• If it grows back, replace it. If the mold grows back, consider replacing the unit, Consumer Reports' tester says.
• Tilt it right. The unit should be tilted slightly toward the exterior, so rain and condensation drain outside instead of pooling inside.

Off-season storage

For units you remove in winter, Consumer Reports says to drain any water inside it, clear off debris, and wipe the internal surfaces clean, dry it by running the fan-only mode for several hours over the course of a few days in dry weather, and store it in a dry spot in an upright position. If you leave it in the window under a cover, don't trap water in it, because mold could grow inside it.

Check for the Midea window AC recall

In June 2025, the CPSC announced a recall of about 1.7 million Midea U and U+ window air conditioners because pooled water in the air conditioners can fail to drain quickly enough, which can lead to mold growth. The firm knew of at least 152 reports of mold in the air conditioners. Consumer Reports lists the brand names they were sold under, including Midea, Comfort Aire, Danby, Frigidaire, Insignia, Keystone, LBG Products, Mr. Cool, Perfect Aire, and Sea Breeze. The remedy is a free repair or a full or prorated refund. If you own a U-shaped window unit, check the model number on the recall page.

Portable units

Portable ACs collect condensate in an internal tank or tray. Consumer Reports warns that standing water in portable units can attract all kinds of mold. Empty and dry the tank as the manual says, especially before storing it.

Ductless mini-split heads hang on the wall, and their coil and blower wheel sit right behind the front cover. If you see black specks on the louvers or blower, or smell mustiness, the same rules apply: the moisture has to drain away, and growth inside the unit needs a deeper clean than wiping the louvers. The manufacturer's manual says what owners can clean (usually the filters) and what needs a technician. Because the blower and coil sit near electronics, this is generally a job for an HVAC contractor.

Table: AC mold removal, what you can do and what you shouldn't.

For hard parts you can reach, the EPA's basic method applies: scrub mold off hard surfaces with detergent and water, and dry completely. The EPA's drain advice is to make sure the drain pans slope toward the drain and the drain is flowing freely, and to make sure the condensate pan drains properly.

Three things not to do:

• No bleach on the unit. UGA Extension says do not use bleach on metals or near the air conditioning system.
• No random sprays. The EPA says a product must be registered by EPA for a specific use before it can be legally used for that purpose. Read the label before spraying anything into an AC system.
• No ozone "shock" treatments. The EPA says when inhaled, ozone can damage the lungs, and at safe levels it does not effectively remove viruses, bacteria, mold, or other biological pollutants.

Turn off central air before any cleanup nearby. UGA says to turn off any central air or heating systems in your home to reduce the spread of mold spores.

Table: AC mold removal cost, national estimates. No source gave Texas-only prices.

Fixr calls HVAC mold work one of the most expensive remediations. We couldn't verify a current independent price for a basic evaporator coil cleaning or for window unit cleaning, so we don't list one. For a small window unit with mold deep inside, compare the cleaning quote to the price of a new unit. See our mold remediation cost guide for the bigger picture.

The equipment and the mold are often two different jobs.

Call a licensed HVAC contractor for the unit itself: coil cleaning, clogged drains, a cracked or rusted drain pan, a unit that's oversized, or water leaking from the air handler. In Texas, TDLR says a license is needed to install, repair, or maintain systems related to air conditioning, refrigeration, or heating. You can check an HVAC license on TDLR's license search.

Call a licensed mold company when mold has spread beyond the unit: to the ceiling under an attic air handler, the closet around it, the ducts, or the walls. TDLR says areas of visible mold of less than 25 contiguous square feet can be cleaned up by people who are not licensed; larger areas generally need a licensed remediation contractor.

Table: Who to call for mold in an AC unit.

Keep testing and removal separate. Texas law says a license holder may not perform both mold assessment and mold remediation on the same project. Our guide on why testing and removal are different companies explains the rule, and mold clearance testing covers how to confirm the job is done.

Find licensed mold testing companies in Houston or San Antonio, and mold removal companies in Houston, Dallas or Corpus Christi. Browse all of Texas, confirm a mold license with our license check, and see how we verify listings.

A moldy AC unit can blow spores into the room. The CDC says some people exposed to mold get a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash, and that people with asthma or mold allergies may react more strongly. In the Midea recall, the CPSC noted 17 reports of consumers experiencing symptoms such as respiratory infections. A doctor, not a mold test, diagnoses mold-related illness. TDLR recommends that people consult a health care provider with health concerns.

• Change filters on schedule.
• Have the system serviced regularly, and ask the technician to check the coil and drain.
• Keep the condensate drain clear and the pan sloped to the drain, per the EPA.
• Keep indoor humidity below 60 percent (ideally between 30 and 50 percent). A dehumidifier helps in damp rooms.
• When replacing equipment, make sure the unit is the proper size for your needs.