Why Is My Air Conditioner Humming?

Air Movement

• Sometimes air that circulates rapidly through the air conditioner can create a low humming noise from gentle vibrations within the vents and other internal components. This is normal behavior for an air conditioning unit, although lowering the fan speed might lessen the effect, if the noise is annoying.

Window Vibration

• Depending on the original installation of the window frame in the wall or how the unit was installed in the frame, a humming or rattling noise can emit from the window frame during air conditioner operation. To remedy this noise, uninstall the unit and start anew. When securing the unit to the window and outside wall, tighten all bolts and screws thoroughly. Skillfully placed weather strips might stop the humming altogether, especially if a strip is added to the windowsill and sash under and above the unit, respectively. Weather strips between the open window, the stationary window and the accordion panels and the window help as well.

Fan Debris

• If dirt or debris is sucked accidentally through the intake grille and wraps around or is stuck inside the fan component, a humming noise might emit from the fan. If you wish to look at the fan yourself, the power should be shut off from the unit to prevent electrical shock. You can remove panels around the front of the air conditioner unit to get to the fan compartment. Once there, inspect the fan motor for mold or debris. If debris is present, such as a plastic bag or pencil, it should be removed. If mold is located, this could also be the cause of noise. A mild soap and a cloth can be used to remove mold.

Duct Expansion

• Ducts inside of an air conditioner can expand and contract during the course of operation, which can cause a humming or clanking noise. This is part of normal function of a central air conditioner or a portable unit air conditioner, as both units feature ductwork. The noise and expansion is common of all ductwork, including large or small, metal or flexible. It's possible to resituate the air conditioner ducts in attempt to squelch the noise, but the noise is non-threatening to the proper function of the unit.