964 alternator belt problem
 

My 964 has been burning alternator belts quickly. In the past month, I've gone through 3 belts already. After driving a couple of miles with a new belt it would suddenly screech and I then smell burning rubber in the cabin leading to the battery indicator lighting up. Note, alternator was rebuilt in the past year.

It happens again today, and after installing my 4th belt I made it idle for 10 minutes - the belt was spinning alright. Switched the car off to check the pulley temperature (both fan and alternator belts/pulleys were ok to touch - heat seemed normal).

I made further testing by idling the car with AC on this time. After a couple of minutes, I noticed the left side of the belt (the one spining from 6 to 12 o'clock side) was wiggly while the right side was firm and straight. I then shut off the engine and noticed the following:
#1 there was rubber powder on the pulley face
#2 the alternator belt/pulley was too hot to touch BUT the fan belt/pulley was ok
#3 the AC compressor body was also too hot to touch but the compressor belt was ok.

I'm quite sure it will suffer the same fate like the previous belts if I left it idling for a couple of minutes more.

Given this observation, why is the AC causing the alternator belt to fail? What needs to be done? Your inputs are highly appreciated.

Are your pulley's adjusted correctly, correct amount of shims? You should have a little under a half inch
of play when you push on a belt. There are cheap belt tension tools you can buy to check. Did this happen on its own, or after you replaced a belt?

If new belts correctly tensioned keep breaking, this link might help you investigate. On a 993 but most things should translate. Repeated alternator belt failures - Rennlist Discussion Forums