How to Clean or Replace an Air Conditioner Filter

Quick answer

To clean an AC filter, turn the unit off and unplug it, slide out the filter, vacuum or rinse it, let it dry completely, and put it back. Window and portable units usually have a washable filter; central air systems usually use a disposable filter that you replace. This guide is for beginners who want to keep their AC cooling well and know when to call a qualified technician.

Safety first

• Window and portable units: turn the unit off and unplug it before removing the filter. If the plug is hard to reach, switch off its breaker.
• Central air: turn the system off at the thermostat before pulling out the filter, so the blower doesn’t pull dust in while the filter is out.
• Only open the filter door, front grille or return grille that your manual describes as user access. Never remove panels that need tools, and never touch wiring or coils behind panels.
• Don’t spray water into the unit itself, and keep water away from the plug and controls.
• If you smell burning or see sparks or scorch marks, stop and call a professional.

Before you begin

Find your owner’s manual and look for the filter section. It will show where the filter is, whether it’s washable, and how often to check it. If you don’t have the manual, find the model number on the rating label and look it up on the manufacturer’s support site.

Know what kind of system you have. Window units often have a filter behind the front grille. Portable units usually have one or two filters on the back or side. Central air typically has a filter in a return grille (a large vent in a wall or ceiling) or in a slot near the indoor unit. Some units have a “filter” reminder light; how it works and resets varies by brand and model.

Possible causes

Here’s why filters matter and what can go wrong.

Things you can check yourself:

• A dusty or clogged filter. It cuts airflow, so rooms cool slowly and the unit works harder.
• A filter in backward or not seated. Air can slip around it, letting dust reach the coils.
• A wrong-size replacement. Gaps around a central air filter let dirty air bypass it.
• A wet filter put back too soon. It can trap moisture and smell musty.
• A missing filter. Running without one lets dust coat the coils.

Problems that need a technician:

• Dirty coils behind panels, which need professional cleaning
• A musty smell or visible mold inside the unit
• Ice on the coils that returns after a clean filter
• A damaged filter frame or housing that’s part of the unit

How to clean or replace the filter

1. Turn off and unplug. Switch the unit off and unplug it, or set the central air thermostat to off. Is the unit fully off? If yes, continue. If you can’t reach the plug safely, switch off the breaker first.
2. Remove the filter. For a window unit, open the front grille or filter door as your manual shows and slide the filter out. For a portable unit, pull out the rear or side filter. For central air, open the return grille or slide the filter out of its slot, and note the airflow arrow printed on the frame.
3. Check how dirty it is. Hold it up to a light. Can you see light through it easily? If yes, a light vacuum may be all it needs. If it’s gray and matted, clean or replace it.
4. Clean a washable filter. Vacuum both sides with a brush attachment, then rinse it with lukewarm water and a little mild dish soap if your manual allows. Rinse from the clean side to push dust out. Shake off excess water and let it air-dry completely, away from direct heat. Is it fully dry? If yes, go to step 6. If not, wait; a damp filter can grow mildew.
5. Replace a disposable filter. Read the size printed on the old filter’s frame, or check your manual, and buy the same size and type. Don’t try to wash a disposable filter unless the manufacturer says it’s washable.
6. Put the filter back correctly. Slide it in fully, with the airflow arrow pointing toward the indoor unit for central air, or facing the way your manual shows. Close the grille or door until it clicks. Does it sit flat with no gaps? If not, remove it and reseat it.
7. Restore power and test. Plug the unit back in or turn the system on. If your unit has a filter reminder light, reset it as the manual describes. Is airflow stronger? If yes, you’re done. If the room still doesn’t cool, see air conditioner not cooling.

Make filter checks part of your seasonal routine; the appliance maintenance checklist can help you remember.

When to stop and call a qualified technician

Contact a qualified HVAC or appliance technician, or the manufacturer’s service network, if:

• The coils behind the filter look heavily dirty, matted or iced over
• You smell mustiness or see mold inside the unit after cleaning the filter
• Cooling or airflow is still weak with a clean filter in place
• You can’t reach the filter without tools or removing panels
• You notice a burning smell, sparks or water near electrical parts
• The unit shows an error code that persists after you look it up in the manual

ENERGY STAR’s maintenance checklist also suggests regular professional checkups for central systems.

FAQ

How often should I clean my AC filter?

It depends on the unit, how often you run it, and your home, such as pets or dust. Many manuals suggest checking room AC filters every few weeks during the cooling season. Central air filters are often checked monthly and replaced when dirty; follow your manual.

Can I use my AC without a filter?

It’s best not to. Without a filter, dust and pet hair collect on the coils, which reduces cooling and can lead to ice or musty smells. Put the filter back as soon as it’s dry.

How do I know which way the filter goes?

Disposable central air filters have an arrow on the frame that should point toward the indoor unit, in the direction the air flows. Room AC filters usually fit only one way; your manual shows how.

Can a dirty filter cause my AC to leak water?

Yes. Poor airflow can let ice form on the coil, and the meltwater may overflow the drain pan. See why is my air conditioner leaking water? for more.