AC noise

[Bo525i]

When I turn on the AC it starts up with a "clunk" and the same happens when I switch it off "clunk", quite loud too plus it does this clunking noise on a regular basis when the engine is idling!

Startup clunk seems to be coming from the front around belts but the turnoff clunk seems to be coming from above the heater valve!

Quite annoying and sounds like something is about to break, but what?

Any pointers?

[Sixdown]

Usually you should hear a click from the compressor, but a clunk isn't normal.

[Bo525i]

Exactly! Maybe the compressor needs replacing..

[The Stretch]

Like sixdown said, the compressor clutch will click when it turns on and off, and especially at idle, it will switch itself on and off as needed. The cabin recirculate will cause a 'thump' sound when it opens and closes the outside air intake flap. This would be by the heater valve. I would start up your car and turn the AC and recirc. on and off in different combinations and listen to the sounds. This should help you figure out what is actually making the sound.

[Bo525i]

I´m going to get hold of a friend to maneuver the controls, its hard to do this and pinpoint the sounds on your own, my arms aren´t long enough.. ;)