Why does my air conditioner rattle when I turn it on?

Common causes of a car air conditioning system making a rattling sound are due to a faulty A/C compressor, a worn V-ribbed belt, or a worn A/C compressor clutch.

Your vehicle's air conditioning system is designed to keep you cool and comfortable as temperatures rise. It is designed to operate quietly and unobtrusively, so an air conditioning system that is in good working order produces little to no noise. However, if you hear a rattling sound when you turn on the air conditioner, it could be a lot of different problems.

While your A/C is technically a separate system, it is connected to the rest of the engine by a V-ribbed belt. The V-ribbed belt is responsible for rotating the A/C compressor pulley and pressurizing the refrigerant lines. The compressor is switched on/off by an electromagnetic clutch.

If you turn on the air conditioner and immediately hear a rattling sound, there are several possible causes:

• CompressorA: If your AC compressor starts to fail, it may make a rattling sound.

• PulleyA: If the compressor pulley bearings fail, they can make noises, usually a screech, roar or squeal.

• belt: If the V-ribbed belt is worn, it may slip when the compressor is turned on, causing noise.

• idler pulley: The noise may be coming from the idler pulley if its bearings fail. The noise started when the compressor was turned on due to the increased load on the engine.

• compressor clutch: The compressor clutch is a wear part, and if it is worn, it may make a knocking sound during operation. In some vehicles, only the clutch can be replaced, while in others, the clutch and compressor need to be replaced.

There are many other potential sources of noise. When the air conditioner turns on, it increases the load on the entire engine. This increased load can cause things like the power steering pump pulley to rattle, loose parts (even a loose hood strut bar can rattle from the extra vibrations generated by your air conditioner). If you hear a knocking sound in your car, call an AutoTachki field technician to check the cause of the sound.