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Maintaining your window unit is essential. A window AC that gets cleaned and stored well can last 8 to 10 years. One that’s left in the window or thrown in a damp garage on its side won’t. This guide walks you through how to clean, dry, reassemble, and store a window AC unit so it’s ready to run next season.
Preparing to Clean Your Window AC Unit
Before you begin, unplug the window unit from the wall and let it sit for at least 15 minutes. The fan blades and electrical components can hold residual current, and the metal coils may still be cold or wet. Move the unit to a flat, stable workspace with good light, like a garage floor, basement workbench, or driveway on a dry day.
Cleaning a window AC isn’t a very risky job, but it can involve mold, mildew, and dust that have spent all season sitting in a damp environment. Mold spores can trigger allergy and asthma symptoms, and prolonged exposure to mildew is genuinely unhealthy. Before opening the unit, put on a fitted dust mask or N95, disposable gloves, and safety glasses. If the unit smells musty, take it outdoors before you start cleaning.
Gather your supplies before you start. You’ll need:
- A soft-bristle brush
- A vacuum with a brush attachment
- A bucket of warm water
- Mild dish soap
- Microfiber cloths
- A low-pressure garden hose
- A replacement filter
- A no-rinse coil cleaner, available at most hardware stores, is helpful but not essential.
Removing the Filter from a Window AC Unit
Most window AC units keep the filter behind the front grille. The grille either snaps off with finger pressure or unclips after you remove two screws at the top corners. Once the grille is off, the filter usually slides straight up or out. Check your manual if you can’t see how it comes free. Forcing a filter out of its slot is the fastest way to tear it or break a clip.
There are two common filter types:
- Disposable filters have a cardboard or thin plastic frame around a paper-style material. They’re meant to be replaced once a year, not cleaned.
- Washable filters have a rigid plastic or metal mesh frame with a foam or synthetic material you can rinse. If you can’t tell which you have, look at the edge.
Cardboard means disposable. Plastic mesh with foam or a sponge-like material means washable.
Once the filter is out, hold it up to a bright light and look for tears, holes, large clumps of debris, and anything that looks like black or green spots. If the filter has tears or holes, replace it regardless of type. If it’s a washable filter with heavy soiling but no damage, that’s fine since it can be cleaned and reused.
Cleaning the Filter and Window AC Unit
If your filter is the disposable type, throw it out and set the replacement aside. For washable filters, rinse with cool tap water from the back side toward the front to push debris out the same way it came in. Once visible dirt is gone, fill a bucket with warm water and a few drops of mild dish soap. Soak the filter for 15 minutes, then rinse and shake off any excess water.
Do not use bleach, ammonia, or harsh degreasers anywhere on the unit. Bleach can cause damage to metal coils and rubber seals. Abrasive scrubbers scratch the housing and can bend the delicate coil fins. Mild soap and a soft brush handle 99% of buildup.
Mold and dirt are easy to tell apart. Dirt is brown, gray, or black, evenly distributed, and rinses away. Mold appears as black, green, or pink spots that don’t rinse out, often with a strong musty smell. If the filter has visible mold, replace it. For mold on the coils, use a no-rinse evaporator coil cleaner per the label directions, then let everything air dry.
Drying time matters. The filter, coils, and interior need at least 24 hours of air drying before reassembly. Storing a damp unit will cause mold to return.
Putting Your Window AC Unit Back Together
Once everything is fully dry, walk through this reassembly checklist before sliding the filter back in:
- Confirm the filter is completely dry
- Look at the coils for any standing water
- Dust the fan blades with a dry microfiber cloth
- Slide the clean (or replacement) filter back into its slot
- Make sure the directional arrows on the frame point the correct way, usually toward the coils
- Snap or screw the front grille back into place
- Plug the unit in briefly and run it on the lowest fan setting for 30 seconds to confirm the fan spins freely and the unit doesn’t make new noises
- Unplug it again
- Wipe down the exterior housing with a damp cloth and mild soap
Pay attention to the side curtains, back vents, and the bottom edge that sits on the windowsill, all of which collect dirt and pollen. Once the exterior is clean and the unit is unplugged, you’re ready to move it to storage.
Where and How to Store Your Window AC Unit
Storage matters just as much as cleaning. The right spot is a dry, indoor location that doesn’t experience big temperature swings. Heated basements and utility rooms are ideal. Attached garages work if they stay above freezing. Avoid sheds, detached garages, and crawl spaces where humidity and freeze-thaw cycles occur.
Always store the unit upright, just as it sat in the window. Window AC units have sealed compressors filled with lubricant. Tipping the unit on its side lets the oil migrate into the refrigerant lines, which can cause damage at startup. If you need to lay it on its side for transport, let it sit upright for at least 24 hours before plugging it in the next season.
Cover the unit with a breathable fabric cover, not plastic. Plastic traps moisture and creates the conditions mold needs to grow. An old bedsheet, a moving blanket, or a purpose-built AC cover all work. Tuck steel wool into the front grille opening if mice are a problem in your storage area.
When reinstalling your window unit, follow these steps:
- Wipe off any storage dust
- Confirm the filter is still in good shape
- Look for nests or droppings inside the housing
Plug the unit in and turn it on to a fan-only setting for a few minutes before switching to cooling. If anything sounds, smells, or feels off, schedule service before running it in the window.
Frequently Asked Questions
How often should I clean my window AC?
Clean the filter every 4 to 6 weeks during the cooling season, and do a deeper clean (coils, drip pan, exterior) once a year before storage. Homes with pets or allergies often need more frequent filter cleaning.
Can I leave my window AC in the window over winter?
It’s not ideal. A window unit left in place loses heat through the housing, lets cold air leak in around the frame, and sees freeze-thaw cycles. Removing it and storing it indoors usually pays off in lower heating bills alone.
What if my window AC smells bad?
A musty smell points to mold growth inside the coils, drip pan, or filter. Clean every surface with a no-rinse coil cleaner, replace the filter, and let everything dry for 48 hours before reassembly. A persistent smell usually means it’s time to retire the unit.
How long does a window AC unit last?
A well-maintained window AC typically lasts 8 to 10 years. If the unit is left in the window year-round or stored damp, you may only get 5 to 7 years of use.
Should I cover my window AC with plastic?
No. Plastic traps moisture and encourages mold. Use a breathable fabric cover or an old sheet instead.
When should I upgrade to central air conditioning?
If you’re running two or more window units, paying high cooling bills, or dealing with rooms that never feel comfortable, it may be time to look into a central AC, ductless mini-split, or small duct system. Hero Home Services offers free in-home consultations to help you find the right fit for your home and budget.
Ready to Upgrade or Service Your AC?
If your window unit is showing its age or you’re tired of cooling your home one room at a time, Hero Home Services can help you find a better solution. From ductless mini-splits to full central AC installs, our licensed Twin Cities technicians will walk you through your options and provide written pricing before any work begins. Call or text us to get started.
