Switch the unit off, lift the front panel, slide out the mesh filters, vacuum or wash them in lukewarm water with mild detergent, and let them dry completely in the shade before you put them back. Samsung says every two weeks and Carrier every 4 to 6 weeks, so check yours in that window.
Why the filters matter so much
The mesh filters behind the front panel of a wall-mounted unit catch room dust before it reaches the indoor coil. When they clog, less air crosses the coil. Cooling drops off, the unit runs longer, and in humid weather the coil can freeze and then drip water down the wall when it thaws.
Carrier calls filter cleaning the single most effective DIY job for keeping a mini-split's airflow up. A lot of the codes on our air conditioner pages, from freeze protection to low airflow, list dirty filters as the first thing to check.
How often to clean them
It depends on the brand and how hard the unit works. Samsung says to clean its wall-unit filters every two weeks, or when CF appears on the display. Carrier recommends checking every 4 to 6 weeks. Friedrich's room air conditioners count fan run time and light CHECK FILTER when a wash is due.
In practice, look at them every two weeks while the unit is working hard in summer or winter. If you can see a gray film on the mesh, wash them.
What you'll need
- A vacuum with a soft brush attachment
- A sink or tub with lukewarm water and a few drops of mild dish detergent
- A soft brush, like an old soft toothbrush or a paintbrush
- A towel, and a shaded, airy spot to dry the filters
- A step stool, since most wall units are mounted high
Take the filters out
Every brand's front panel is a little different, so keep the owner's manual handy the first time. The steps below cover most wall-mounted indoor units.
Turn the unit off with the remote and wait for the louver to close. Then switch it off at the breaker, or unplug it if it has a plug, as Samsung's instructions say.
Open the front panel as your manual shows. On many models it lifts from the bottom edge. On Samsung wall units you press the hinges until they click, then lift the cover and prop it with the strut.
Slide the mesh filters out. On many units there's a tab at the bottom of each filter that you lift slightly before pulling it down and out.
Some units also have a secondary filter, such as a carbon or fine-particle filter. Samsung warns that the inside surface of the PM 1.0 filter on some of its models is sharp enough to cut your fingers. Check your manual before washing any secondary filter.
Clean and dry them
Start by taking the loose dust off with a vacuum or a soft brush. If the filters are only lightly dusty, that may be all they need.
For anything heavier, wash them. Samsung's method is to soak the filters for about 30 minutes in lukewarm water with a mild detergent, then rinse them under running water and work stubborn dust out with a soft brush. Skip hot water and strong cleaners.
Shake off the water, pat them with a towel and let them air-dry in a shaded, well-ventilated spot. Samsung says to keep them out of direct sunlight and to make sure they're completely dry before they go back in, or the unit can start to smell. Samsung's leak guide adds that drying them in a small, humid room causes odors too, and suggests running the unit in Fan mode for about 30 minutes after cleaning to dry out any leftover moisture inside.
Wipe the unit and reinstall
While the filters dry, wipe the cabinet with a dry cloth or go over it with a small vacuum, as Carrier suggests. Don't spray cleaner into the unit and don't poke at the coil fins behind the filters.
Slide each filter back into its guides, the same way round as it came out. Close the front panel until it clicks, restore power, and run the unit to confirm it starts normally. If your unit shows a filter reminder, your manual explains how to clear it.
What filter cleaning won't fix
Clean filters keep the coil from getting buried, but they can't clean the coil or the blower wheel behind it. If you see dust caked on the coil, black spots on the blower, or the unit still smells musty with fresh filters, schedule a professional cleaning. A contractor quoted in Carrier's maintenance guide says the evaporator coil should still be cleaned professionally once or twice a year.
If the unit still cools poorly with clean filters, or still leaks, our guides on an AC blowing warm air and an AC leaking water cover the next checks.
When to call a professional
Call an HVAC technician if the coil behind the filters is caked with dirt or growing mold, if the unit still freezes up or leaks with clean filters, or if the front panel or filter guides are broken. Deep cleaning of the coil and blower wheel requires taking the unit apart.