Why Is the Central AC Humming?

Air Ducts

• Humming may be caused by a loose flap in the air ducts. Follow the air ducts along while the air conditioner is running and listen for changes in tone. If the humming gets louder in one area, check for a loose flap or piece of metal. Secure it if possible or make a small dent in the area to allow the air to move over the piece.

Hardware

• Humming or rattling during central AC use may indicate that there are areas of hardware that are loose. Turn off and unplug the air conditioner prior to checking joints, nuts and bolts and tightening as necessary.

Air Flow

• An obstructed air flow may also be the cause of noise coming from the central air conditioning unit. Inspect return air grilles throughout the home and remove items that may be blocking the air, such as furniture, drapes, toys or anything that can cause a rattling or humming noise.

Dirty Components

• Humming may be caused by a dirty fan. If possible, turn off and unplug the air conditioner and wipe the fan blades with a clean, damp cloth to remove excess dust and lint. The outdoor condensing coil may also be dirty, reducing indoor air flow and causing noise. Disconnect power and clean the condenser coils with a soft brush.