Remove mold from a window AC unit by cleaning the filter, coils, and drain pan with vinegar or a commercial mold cleaner
Mold grows in window air conditioners because they trap moisture and stay cool — exactly what mold needs. The filter catches dust and debris, the evaporator coils collect condensation, and the drain pan holds water that should flow outside. If any of these parts stay damp and dirty, mold will colonize them within weeks. You can stop it by cleaning these three areas yourself with tools you likely have at home.
The job takes 30 to 45 minutes and requires no special skills. You will need a screwdriver to open the unit, a vacuum or brush to clear debris, and either white vinegar or a commercial mold cleaner. If the mold smell is strong or the growth covers more than a few spots, the unit may need professional cleaning or replacement — but most window AC mold can be handled at home.
Key Takeaways
- Unplug the unit before you open it, and let it sit unplugged for at least 30 minutes so the coils dry slightly.
- The filter is the easiest part to clean: vacuum it, wash it with vinegar solution, and let it dry completely before reinstalling.
- The evaporator coils and drain pan require a brush or old toothbrush and vinegar or mold cleaner applied directly to the growth.
- After cleaning, run the unit on fan-only mode for 15 minutes to dry the interior before closing it up.
- Clean the filter monthly and the coils and pan every three months to prevent mold from returning.
Unplug the unit and remove the front cover
Turn off the air conditioner and unplug it from the wall outlet. Wait at least 30 minutes before opening the unit — this allows the coils to dry slightly and makes the mold easier to see and remove. Do not skip this step; working on a live electrical appliance is dangerous.
Locate the screws or clips holding the front cover or filter frame in place. Most window units have two to four screws on the sides or bottom. Remove them and set them aside in a small container so you do not lose them. Gently pull the cover away from the unit. If it does not move easily, check for additional fasteners you may have missed.
Vacuum and inspect the filter
The filter is usually a flat, accordion-style panel behind the front cover. Hold it up to a light source and look for mold — it appears as black, green, or brown spots or a fuzzy coating. Vacuum both sides of the filter with a handheld vacuum or the brush attachment of a full-size vacuum. Work from top to bottom to push debris downward.
If the filter is visibly moldy or very dirty, wash it. Mix equal parts white vinegar and water in a spray bottle or bucket. Spray or soak the filter, let it sit for 10 minutes, then scrub gently with a soft brush or cloth. Rinse it under cool running water until the water runs clear. Hang it vertically to dry completely — this usually takes 2 to 4 hours. Do not reinstall a damp filter; it will grow mold again when ready.
Clean the evaporator coils with vinegar or mold cleaner
Behind the filter, you will see the evaporator coils — thin metal fins arranged in rows. This is where most mold grows because condensation collects here constantly. Look for black or green spots, a slimy coating, or a musty smell coming from this area. If you see mold, you need to clean it.
Spray the coils directly with white vinegar or a commercial mold cleaner designed for AC units. Let it sit for 10 to 15 minutes. Use an old toothbrush or a soft-bristled brush to gently scrub the fins. Work carefully — the fins are delicate and bend easily. Wipe away the loosened mold and cleaner with a damp cloth. If the mold is heavy, repeat the spray-and-scrub step once more.
Do not use a pressure washer or high-pressure water spray on the coils — you will damage them. Vinegar is safe and inexpensive; if you prefer a commercial product, look for cleaners labeled for air conditioner coils or HVAC systems.
Empty and clean the drain pan
Below the coils sits the drain pan, a shallow tray that collects condensation. This pan often holds standing water and is a common mold hotspot. Locate it — it is usually at the bottom of the unit, beneath the coils. If water or sludge is sitting in it, that is a sign mold is present.
Carefully remove the pan if it is removable, or clean it in place. Empty any standing water into a sink. Spray the pan with vinegar or mold cleaner and scrub it with a brush. Pay attention to the corners and edges where mold hides. Rinse it thoroughly with water and dry it with a cloth. If the pan is removable, let it air-dry completely before reinstalling it.
Check the drain hole or tube that allows water to exit the unit. If it is clogged with debris or algae, clear it with a pipe cleaner or thin brush. A blocked drain forces water to sit in the pan, which guarantees mold growth.
Reassemble and run the unit on fan mode
Once all parts are clean and dry, reinstall the drain pan if you removed it. Slide the filter back into its frame, making sure it sits flat and fully inserted. Replace the front cover and tighten all screws. Do not overtighten — you only need them snug enough to hold the cover in place.
Plug the unit back in and turn it on. Set it to fan-only mode (not cooling) and run it for 15 minutes. This dries the interior and helps clear any remaining moisture or cleaner residue. After 15 minutes, turn it off and let it sit for a few minutes before switching to normal cooling mode.
Prevent mold from returning with regular maintenance
Mold will come back if you do not maintain the unit. The easiest prevention is a monthly filter check: vacuum it every month during cooling season, and wash it every two to three months. A clean filter reduces the debris that feeds mold and improves airflow, which helps the unit dry between uses.
Clean the coils and drain pan every three months, or more often if you live in a humid climate or run the unit constantly. If you notice a musty smell returning within a few weeks of cleaning, the drain may be clogged again — check and clear it. At the end of each cooling season, run the unit on fan mode for 30 minutes before shutting it down for the year. This dries out the interior and reduces mold growth over the off-season.
If mold returns repeatedly despite regular cleaning, the unit may have a design flaw that traps moisture, or the drain system may be permanently compromised. In that case, replacement is often more practical than constant cleaning.
Frequently Asked Questions
Is it safe to use bleach to clean mold in an AC unit?
Bleach is not recommended for AC units. It can corrode metal coils and fins, and the fumes can damage the unit's electrical components. Vinegar or commercial AC coil cleaners are safer and equally effective at killing mold.
What if the mold smell is still there after I clean it?
The smell may linger for a day or two after cleaning. If it persists beyond that, the mold may be deeper inside the unit where you cannot reach it — in the ductwork, behind the coils, or in the compressor housing. A professional AC technician can open the unit further and clean these areas, or you may need to replace the unit.
Can I run the AC while it is wet after cleaning?
No. Running the unit while parts are wet can damage electrical components and spread mold spores. Always let the filter, coils, and pan dry completely before reassembling and turning the unit back on. The fan-only mode step at the end helps finish the drying process safely.
How often should I replace the filter instead of cleaning it?
Most reusable filters can be washed and reused many times. Replace the filter only if it tears during cleaning, if the material breaks down, or if washing no longer removes the dirt and smell. Check your unit's manual for the filter type — some units use disposable filters that should be replaced monthly.
Will cleaning the AC unit reduce the mold smell in my room?
Yes, if the smell is coming from the unit itself. Once you clean the coils, drain pan, and filter, the musty odor should disappear within a few hours. If the smell persists or returns quickly, the mold may be in the window frame, wall, or elsewhere in the room — not in the AC unit.