Squeaking & Rattling at Idle From an Air Conditioner

Ductwork

• Unsecured ductwork in the attic or crawl space of your home or office can cause a squeaking or rattling noise, even when the air conditioner unit is off or not in use. Ducts of all varieties, including metal and flexible ducts, expand and contract over time. This can cause shifting, which results in noises. Vibrations from the building’s other appliances can cause the ductwork to shake and rattle as well. You can secure the ducts to support beams or other framework with special straps or duct tape.

Thermostat

• It’s possible for the compressor or condenser fan to continue to run, long after the unit has shut off, if the thermostat is broken or disconnected from either of these two air conditioner components. This could cause either component to make noises while it runs, even though the other component has shut off after the desired thermostat setting has been reached. You can turn the thermostat up while the unit runs to test the connections. After the increased thermostat setting reaches a temperature mark that’s above room temperature, both the compressor and the fan should turn off. If they don’t, the thermostat is malfunctioning and requires repair.

Debris

• All kinds of debris can enter the unit through the intake grille and jam up the fan component. This causes squeaking or rattling as the fan struggles to turn. Remove the air conditioner fan-housing panel to access the fan housing. Search for trash, such as plastic bags or sticks, surrounding the fan component and remove it. It’s also possible for a small creature to make its way inside the unit or ductwork and get trapped.

Fan Component

• If the air conditioner features a fan-only function, this could be used to circulate the air in the room while the cooling component remains idle. There are a number of reasons why a fan component might squeak or rattle, including debris and dry ball bearings. If the unit squeaks, the cause is likely the fan component ball bearings. When forced to turn, dry ball bearings can emit a shriek or a shrill noise. With the housing panel on the air conditioner removed, you can twist the fan blades around to check for noise or resistance from the ball bearings. To eliminate the noise, inserting electric motor oil into the ball bearing lubrication ports should help.