A/c woes

[selavia]

Turned on the A/C yesterday and when the compressor kicked, it sounded like a child was banging two metal pots together. It was terrible; when I accelerated past 1500rpms it went away, but everytime I passed 1000-1400 it was the most God awful noise.

Are the Compressor bearings completely shot? The A/C still blew cold as ice.

 

[selavia]

Additional note; turned the a/c on and watched the a/c compressor pulley. When I revved the engine and it made the noise, it only made the noise when the following conditions were met:

1. While the a/c compressor wheel was spinning,
2. the inside wheel would stop intermiditely (sp?) (as if the gear to what made it spin was stripped)

So now I'm thinking it's time for an A/C compressor, any thoughts?

 

[Big Daddy]

The pulley stops when the compressor is not engaged, it is an electrical switching device (not sure how to explain or if we are talking about the same thing) but you description of the pulley sounds normal. The nosie sounds like faulty bearings. (I am no expert on AC units, I would have it looked at) Sorry I am no help!

 

[selavia]

What I mean is the following:


I have two belts up front; the Serpentine Which is connected to damn near everything (alternator, crankshaft, power steering, etc). Then in front of that belt is the A/C compressor belt. Two pulley and an "adjuster" touch this belt. The (I believe) crank pulley works fine. The other pulley is the one that I am referring to and the following description is how it works.

(1) When the A/c is off:
The out side of the pulley (the grooved circle that is actually touching the belt spins. It spins whenever the engine is on. The inside of this pulley (there are some screws etc, that hold it in) does NOT spine when the A/C is off.
I know that this is normal

(2) When the A/C is ON & the compressor is off:
The conditions are the same as described in subsection (1).

(3) When the A/C is ON & THE COMPRESSOR IS ON:
The inside of this pulley spins in tandem with the outside of the pulley (outside of pulley being described as the grooved bit that actually touches the belt).
When I revved the engine (presummably to 1100 rpms), it made that awful sound and the INSIDE of that pulley stopped or hestitated or paused or was interrupted in some way and stoped moving for the briefest of moments. Then within a second, the sound goes away and the inside of the pulley spins in tandem with the outside of the pulley until the compressor switches it self off.

Is this clearer, Dan?

 

[Kirby]

One of two possibilities:
1. The compressor is hosed and binding up. Could be bearings, or some other internal problem.
2. It should be an electric clutch. When the compressor needs to run due to a cooling load, the electric clutch activates and drives compressor. If the electric clutch is failing, it could slip and cause the noise.

Note that this is from my general knowledge of car A/C systems, and not specific knowledge of BMW A/C.

 

[selavia]

Let me add one more fact that my fried brain forgot earlier:

Since I've owned the car, whenever I have had the A/C on and the compressor is on, it makes an "Ooooong Onnng" Sound. And the intensity of the sound changes as the rpms increase. So I've always known that sooner or later something would have to be replaced; now it's a matter of diagnosing.

If this fact helps any or sheds new light, please comment.

Thanks Dan & Kirby!