So i removed the compressor and had a close look at the bracket and all is good (see pic). I reassembled everything and installed a new belt I picked up from the local Porsche dealer. I tightened the belt to a point that there is very little deflection (half a belt thickness) when pressed hard with a thumb. Frankly any tighter and I'm afraid of wreaking the bearing on the compressor. I took a video of the belt when the car is running and you will noticed a vibration in the belt. I rechecked the pulleys and they are in perfect alignment. I realized that the straight edge that I had used was not so straight so I found another and rechecked the pulleys and the set up was perfect. The belt has stayed on all for over 100 miles, so at least that's good.

link to video https://www.youtube.com/watch?v=FSr8...ature=youtu.be

Any suggestions as to why the belt would vibrate like that.

 

Something sounds extremely noisy - is that the airpump on its way out (or out already)?

I'm not sure the vibration is so unusual - there is no tensioner and the pumping action of the compressor varies the loading dynamically - at different speeds this has different resonant effects with the belt configuration. To me it doesn't seem that excessive.

Alan

 

whats interesting is it doesn't seem to matter if the a/c is in-gauged or not...its almost mike the Compressor pulley is holding the belt too long...like its sticky. I didn't think the car was making excessive noise. It certainly sounds worse in the video. But thanks for pointing that out. I'll have another look...with a better ear.