My High Efficiency Central Air Unit Fan Is Making a Loud Noise

Debris

• If you hear a rattling noise inside the outside air conditioner unit, a piece of debris, such as a stick, leaves or piece of plastic, might have been inserted through the vents. If you suspect this to be the case, remove panels on the unit to access the fan housing. Before removing panels, confirm that the power is turned off to avoid electrocution. All debris should be removed from the unit to avoid sounds or damage, and to enhance cooling power.

Ducts

• Duct work of all types, including metal and flexible, can cause noise as it expands and contracts during operation. Ducts are the passageways that deliver air from the unit to different rooms in the home. If the ducts aren’t fastened securely to the structure of the home, a rattling noise can be produced as the duct work vibrates. Search attic and crawl spaces to locate ducts within the home. If the ducts are loose, they can be attached to support beams and walls with duct tape or special straps.

Fan Housing

• An improperly installed condenser fan can cause a loud noise inside a central air conditioner unit and can damage the fan. If you hear the fan making a repetitive noise within the unit, remove panels to access the housing. Spin the fan around by hand to see if it strikes the side of the fan housing. If so, uninstall the fan from the fan motor and reinstall it correctly. The fan should spin freely.

Ball Bearings

• Dry ball bearings can generate a squeaking noise and cause the unit to operate poorly. After air conditioner panels are removed, turn the fan by hand to determine if the ball bearings hinder the performance of the fan. If lubrication is required, electrical motor oil should be applied correctly into the lubrication holes of the fan axle. The oil is worked into the bearings as the fan spins and the noise will subside.