Quick checklist by frequency
| When | Task |
|---|---|
| Monthly while in use | Clean or replace the filter; wipe the front grille; check for water or odors |
| Start of season | Inspect cord and plug; clean coils and fins; check drainage and tilt; check seals; test the unit |
| Mid-season | Look for ice, drips on the sill, musty smells; recheck the filter |
| End of season | Clean and dry the unit; store indoors or cover it |
Before you start
- Unplug the unit before removing panels or cleaning anything internal. Never clean around live electrical parts.
- Check the owner’s manual for model-specific instructions.
- Window units are heavy (many weigh tens of pounds). Get help lifting and keep a firm grip, especially above ground level. If removing the unit from an upper-story window feels unsafe, hire someone.
- Coil fins are thin and sharp. Wear gloves and go gently.
Monthly tasks during the cooling season
Clean the filter
Most window units have a washable filter behind the front panel. Slide it out, wash it with mild soap and warm water, let it dry completely and put it back. Many sources suggest about once a month during heavy use, or as the manual says. If the filter is torn or damaged, replace it. A clogged filter restricts airflow and can make the coil freeze, which leads to dripping.
Wipe the grille and check for blockages
Remove dust and pet hair from the front intake and outlet with a soft cloth or vacuum brush.
Check the pan and drainage
Some units drain out the back through a hole or small tube, while others have a pan that must be emptied. Know which you have, and keep the drain opening clear. Many manufacturers want the unit to tilt slightly toward the outside so condensate drains outdoors, and a unit tilted toward the room can drip inside. Follow the installation instructions for your model.
Start-of-season tasks
Inspect the cord and plug
Look for fraying, cracks, burn marks or a plug that gets hot. Do not use a unit with a damaged cord. Cord replacement is best done by a professional. Avoid extension cords and power strips for window ACs; many manufacturers specifically advise against them. Check the nameplate for the voltage and circuit needs, since larger units may need a dedicated outlet.
Check for nests and debris
If the unit stayed in the window over winter, check inside for insect nests, leaves and debris before powering it on.
Clean the coils and fins
With the unit unplugged and removed from its case according to the manual, gently brush or vacuum dust from the evaporator (indoor side) and condenser (outdoor side) coils. A fin comb can straighten bent fins. Do not use high-pressure water on the electrical parts, and avoid soaking the unit. Dry it thoroughly before use.
Check the window seal and support
Inspect the side panels and foam or weatherstripping for gaps. Seal gaps to stop hot air and insects from entering. Make sure the unit is supported securely; larger units may need a bracket. Check local rules, since some buildings require brackets.
Look for mold
Check the filter, pan and coil area for black, green or musty-smelling growth. Light mold on hard surfaces can be cleaned with soap and water or a product made for the purpose, following label directions. Do not mix cleaning chemicals, such as bleach with vinegar or ammonia. Wear gloves and a mask and ventilate. If growth is heavy or you are sensitive to mold, get help.
Test it
Plug it in and run it. Cooling should start within a short time, and you should not hear grinding or rattling. If it blows warm air or makes unusual noises, stop and consider a technician. Weak cooling can be a sign of a sealed-system problem that is not a DIY job.
Mid-season checks for leaks
- Look for ice on the front coil. If outdoor temperatures are cool, window units can ice up. Switch to fan mode to let it thaw.
- Check the sill for drips, staining or soft wood (see window repair vs replacement if the frame is damaged).
- Smell for musty odors, which can mean stale water or mold.
For causes of dripping beyond window units, see our guide to reasons your AC is leaking water.
End-of-season tasks
- Clean the filter and coils and let everything dry fully.
- Store the unit indoors in a dry place if you can, or cover the outside of the unit and seal the gap around it so cold drafts, moisture and pests stay out.
- Keep it upright in storage unless the manual says otherwise.
Repair or replace
Lifespan estimates vary. One home inspector quoted by AARP suggests a window unit can last roughly five to ten years with good care. Actual life depends on use, climate and maintenance.
The “$5,000 rule” is a rule of thumb sometimes quoted for larger central systems: multiply the age by the repair cost and compare to about $5,000. Window units cost far less, so a simpler approach is to compare the repair quote with the price of a comparable new unit, and consider the age and efficiency of what you have.
When to call a professional
- Damaged cord, plug or electrical smell
- Breaker tripping when the unit starts
- Ice that keeps returning after cleaning the filter
- Suspected refrigerant leak (weak cooling, oily residue, hissing)
- Water leaking inside even though the unit is tilted correctly and clean
- Unsafe installation, especially above the ground floor
FAQ
What is the 3-minute rule for air conditioners?
It is a common guideline to wait a few minutes after turning an AC off before turning it back on, so the compressor is not restarted against high pressure. Many modern units have a built-in delay. Check your manual.
What is the average lifespan of a window AC?
Often described as about five to ten years with proper care, though results vary.
How do I maintain a window unit air conditioner?
Unplug it, clean the filter monthly, clean the coils each season, keep the drain clear, check seals and the cord, and store or cover it in the off-season.
My window AC is dripping. What should I check?
Check the tilt, the drain hole, the filter and the coils, and look for ice. If it still drips, see our article on AC duct and vent dripping only if you have central air; otherwise consider service for the unit.