What does the belt that drives the aircon compressor also drive?

Why not look? It's hardly difficult.

It also varies by make of car and possibly model too.

However *as a rule* AC usually has its own belt as it is often an option on cars so saves a total re-design.

as a rule there is one belt that drives all the peripherals on modern motors. where a/c is not specified as an option, the compressor is not fitted and a shorter belt is therefore used. you may be able to get around the problem by fitting a belt of the length specified for a car without a/c. i know this works on many mercedes. have a look at the belt journey around the various pulleys, you should be able to work it out.

My AC belt broken weeks ago. For my 99 528i obviously it only drives the AC. I drove the car OK w/o AC for a few days.

Okay - it looks that we too when looking at it, but it is rather tight down there as partly hidden under the engine.

I'll keep my fingers crossed that it last until I get it past the garage.

Well... It is partly hídden under the engine - so it's not THAT easy to see. However it does actually look like the belt is used only by the a/c but I was not sure.

Sure thing... That's why I posted in the bmw newsgroup and mentioned that it is a 2002 E39 530dA touring. It does vary for sure, I also have a Peugeot 406 coupe 3.0 and on that it is the same belt that drives a/c and the generator... Clever French design ;-)

I don't think that they sold a lot of them without a/c - I think the manual aircon was standard. Anyway, what you say does make sense.

Apparently BMW doesn't follow your rule. I've never seen a BMW that had one belt and AC.

This ain't a mercedes newsgroup BTW..