How to Remove Mold from a Window Air Conditioner

Mold grows in window air conditioners because they trap moisture

Window air conditioners collect mold because they pull warm, humid air from your room and cool it by running it over cold coils. That temperature drop causes water to condense on those coils — the same way a cold glass sweats on a hot day. If that water doesn't drain properly or sits stagnant, mold spores land on it and start growing. You'll see black or green spots on the filter, inside the unit's casing, or on the fins (the thin metal blades that look like a comb).

The mold itself isn't always dangerous, but it can trigger allergies or asthma, especially if you run the unit in a bedroom where you breathe the air for eight hours. Removing it is straightforward and takes about 30 minutes. You don't need to replace the whole unit unless the mold has spread deep into the coils or the unit is more than 10 years old.

Key Takeaways

Unplug the air conditioner before you touch any internal parts, and let it sit for at least 15 minutes so the coils are no longer cold.
Remove and wash the filter with warm soapy water, or replace it if it's torn or heavily spotted — filters cost $10 to $30.
Spray the coils and fins with a mold-killing solution (white vinegar, hydrogen peroxide, or commercial coil cleaner) and let it sit for 10 minutes before wiping.
Clean the drain pan and drain hole at the bottom of the unit so water can flow freely and won't pool where mold grows.
Run the unit on fan-only mode for 15 minutes after cleaning to dry out the interior before you use it normally again.

Unplug the unit and let the coils warm up before you start

Unplug the air conditioner from the wall outlet. This is non-negotiable — you're about to spray liquid near electrical parts, and you don't want the unit running while you work. Wait at least 15 minutes. The coils inside are very cold while the unit is running, and touching them or spraying them when ready can cause condensation to freeze on them, which makes mold worse. Waiting lets them warm to room temperature.

While you wait, gather your supplies: a soft brush or old toothbrush, clean rags or paper towels, a spray bottle, and a mold-killing liquid. White vinegar works well and costs almost nothing. Hydrogen peroxide (the 3% kind from a drugstore) also kills mold. If you prefer a commercial product, look for coil cleaner or mold-killing spray at a hardware store — brands like Frost King or Frost King ACF-19 are made for this job. You'll also need a small bucket of warm water and dish soap.

Remove and clean or replace the filter

Open the front panel or cover of the air conditioner. The filter is usually a flat, accordion-style panel that slides out from the front or side. Pull it straight out gently — it may be dusty. Hold it up to a light and look through it. If you can see light coming through clearly, it's not clogged. If it's dark and you can barely see light, it needs cleaning or replacing.

If the filter is intact and not heavily molded, wash it under warm running water with a drop of dish soap. Use your fingers or a soft brush to work the soap through the pleats. Rinse until the water runs clear. Lay it flat on a clean towel to dry completely — at least an hour — before you put it back. If the filter is torn, has large moldy patches, or is more than a year old, replace it. Filters are inexpensive ($10 to $30) and widely available online or at hardware stores. Check your unit's model number on the back or side to order the right size.

Spray the coils and fins with a mold-killing solution

With the filter out, you can now see the coils and fins inside the unit. This is where most of the mold hides. Fill a spray bottle with your chosen solution — white vinegar straight from the bottle, or hydrogen peroxide from the drugstore. If you're using a commercial coil cleaner, follow the label instructions for dilution.

Spray the coils and fins thoroughly until they're wet but not dripping. The solution needs contact time to kill the mold, so let it sit for 10 minutes. Don't wipe it off when ready. After 10 minutes, use a soft brush or old toothbrush to gently scrub the fins — they're delicate and bend easily, so use light pressure. Wipe away the loosened mold and solution with a clean, damp rag. You may need to spray and wipe a second time if the mold is heavy. Let the interior air-dry for a few minutes before you reassemble the unit.

Clean the drain pan and drain hole

At the bottom of the window air conditioner, there's a small pan that collects condensation water. This pan is often the source of mold because water sits in it. Locate the drain hole — it's usually a small opening at the lowest point of the pan. Use a straightened paperclip or a thin brush to poke through the hole and clear any debris or algae that's blocking it. If the hole is clogged, water backs up and pools, creating a mold farm.

Wipe out the drain pan with a damp cloth and a little vinegar or soapy water. If you can access it easily, you can remove it and rinse it in a sink. Make sure the pan sits level so water drains toward the hole, not away from it. If the pan is cracked or the drain is permanently blocked, you may need to replace the pan — contact the manufacturer or a local appliance repair shop for the part number.

Reassemble the unit and run it on fan mode to dry

Slide the clean or new filter back into place, making sure it's seated fully and facing the right direction. Most filters have an arrow printed on the frame showing which way the air should flow — it should point into the unit, not out. Close the front panel or cover. Plug the unit back in.

Before you use the air conditioner normally, run it on fan-only mode (no cooling) for 15 minutes. This dries out the interior and helps prevent mold from regrowing when ready. After 15 minutes, you can switch it back to cooling mode and use it as usual.

Prevent mold from coming back

Mold returns if moisture builds up again, so prevention is easier than cleaning. Run your air conditioner on fan mode for 10 to 15 minutes after you turn off the cooling — this dries the coils and drain pan. If your room is very humid (above 60% humidity), consider running a separate dehumidifier or opening a window to let moisture escape. Clean or replace the filter every month during cooling season. If you live in a very humid climate or don't use the unit often, clean it every two months instead of waiting for visible mold.

At the end of the cooling season, before you store the unit, run it on fan mode for 30 minutes to dry it completely. Store it in a dry place, not a damp basement or garage. If you're leaving the unit in the window year-round, cover it with a weatherproof cover to keep rain and humidity out.

When to call a professional

If mold is visible deep inside the coils (not just on the surface), if the unit smells strongly of mold even after cleaning, or if water is leaking from the unit, call a local appliance repair technician. They have tools to clean coils that you can't reach and can test whether the drain system is working. If the unit is more than 10 years old and mold keeps returning, replacement may be cheaper than repeated repairs.

If you have a severe mold allergy or respiratory condition, consider wearing a dust mask while cleaning, or ask someone else to do it. The mold spores released during cleaning can trigger symptoms in sensitive people.

Frequently Asked Questions

Is mold in a window air conditioner dangerous?

Mold itself is not toxic, but inhaling mold spores can trigger allergies, asthma, or sinus problems, especially with prolonged exposure. If you have asthma or a mold allergy, clean the unit regularly and consider replacing it if mold returns frequently despite your efforts.

Can I use bleach to kill mold in an air conditioner?

Bleach is harsh on metal and can corrode the aluminum fins and coils. Stick with white vinegar or hydrogen peroxide, which are gentler and just as effective. If you use a commercial cleaner, check the label to make sure it's safe for air conditioner coils.

How often should I clean my window air conditioner?

Clean or replace the filter every month during cooling season. If you live in a humid climate or the unit sits unused for long periods, inspect it every two weeks. A full internal cleaning (coils and drain pan) is needed only when you see visible mold or smell a musty odor.

What if water is leaking from my air conditioner after I clean it?

The drain hole may still be blocked, or the pan may be tilted. Check that the unit is level and that the drain hole is clear. If water still leaks after you've cleared the hole and leveled the unit, the pan may be cracked or the drain tube may be disconnected — contact a repair technician.

Can I prevent mold by running the air conditioner less often?

Running it less often actually makes mold worse because moisture builds up in the stagnant coils. Instead, run it regularly and use fan mode at the end of each day to dry the interior. If you're not using the unit, store it in a dry place and cover it.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.