rattling only with ac on
 

so i have narrowed down a rattle to only when the ac is on which leads me to believe it is the compressor that is rattling and not the a/c belt system because that is spinning even when the a/c is off. am I correct? or could it still be one of the pulleys in the a/c belt system?

If it is the compressor, is there any way around buying a new compressor? they're ridiculously expensive and ill just live with it if it comes down to that.

I live in arizona so the a/c had been perpetually on since i bought the car. Now that im experimenting what happenns when it off I have noticed that it shifts a lot rougher with the a/c off. Is this normal?

I also have this problem on a '99 328i. When I turn the a/c on, it rattles, as you say, or chatters or knocks as I would describe it. First, thing I did was replace the a/c belt tensioner (and the other tensioner and pulley) but that didn't resolve it and the old a/c belt tensioner didn't seem to be worn out.
It makes this sound upon a/c startup and most typically when sitting at idle. Not dedectable while driving.
The a/c works fine and there are no codes being thrown.
Anyone else have this problem or know of a solution or way to investigate further?

Thanks

I get quite a bit of noise from it as well.

3 people so far with the same problem, i was thinking of changing my tensioner as well, but if it doesnt fix it then i guess im glad i didnt waste my money on it. Anyone know what is causing this common problem?

I had this same problem, a rattling noise only when the A/C compressor was on. I lived with it for a little bit but it started to trigger my SES light. I eventually ended up replacing it. The noise is being caused by a bad pulley on the A/C compressor. Unfortunately, the only fix is to replace the entire compressor.

im not positive myself but isnt that called the comrpessor clutch? cant that be replaced without replacing the whole compressor unit?
?

The A/C compressor is all or nothing. I suppose you could find a shop to tear it down and rebuild it for you, however. I'd save that headache and just buy a new one.

yeah my compressor clutch went. it would click when i turned on the ac and also when i hit the brakes because it was shifting. just got a new compressor, although a guy did say he couldve just replaced the clutch for me.

how much did you pay for the new compressor?

got one out of a junkyard...paid 60 bucks for it and 100 for the install.

when you buy that from a junkyard, you are really just gambling that a) it works, and b) it too doesn't rattle when turned on like the current one.

Am i correct? or can you return them if its not performing right?

nope no guarantees...but wth it was 60 bucks ya know? no biggie

I have the same prob in 99 328i, it's caused by bad Pulley, you're right. And I agree for not rebuild the comprosser, just buy a new one, sence rebuilding will cost aproxmitly same price of new one, and may wont last long with you like the new.