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Air Conditioner Air filter: What It Does and Signs It's Failing

The mesh screens that snap in behind the front panel of a wall unit or the return grille of a ceiling or ducted unit. They trap dust before it reaches the coil and blower.

How it works

All the air the indoor fan moves passes through the filter. A clogged filter starves the coil of air, which hurts comfort and can freeze the coil or overheat a heat pump.

Signs it is failing

• Weak airflow from the indoor unit
• Dust visible on the mesh
• Ice on the indoor coil
• Overheating codes in heat mode
• A filter-clean reminder light

LG and Daikin list clogged filters among the causes of overheating and high-pressure codes in heat mode.

Can you replace it yourself?

Turn the unit off, lift the front panel, slide out the filters and rinse them in lukewarm water. Let them dry before refitting. DOE suggests cleaning every month or two during heavy use.

Buying the right part

Washable mesh filters last a long time if you don't tear them. Replace a torn one by ordering for your indoor unit's model number.

Error codes linked to the air filter

• A5Freeze-up or overheat protectionDaikin
• E1Short cycling or a sensor fault, depending on modelFriedrich
• CHECK FILTERFilter cleaning reminderFriedrich
• E1High pressure protectionGree
• E3Low pressure protectionGree
• E2Indoor coil freeze protectionGree
• E8High temperature protection from low indoor airflowGree
• CH04Drain problem or water tank fullLG
• CH61Unit overheatingLG
• EH 03Indoor fan speed out of rangeMidea
• PC 08Over-current protectionMidea
• P6Freeze or overheat protectionMitsubishi Electric
• U1 / UdHigh pressure or overheat protectionMitsubishi Electric
• CFFilter cleaning reminderSamsung
• E153 / E665Drain pump or float switch problemSamsung

Last reviewed 2026-10-19.