Great Information MrMerlin - I tucked a copy of this away in my 928 DNK (Did Not Know) Files for myself..... The condensed information on the later 928's will be a nice addition to have on hand.
A couple of years ago a buddy had turned his 89 S4 over to an A/C shop for a minor system recharge. Finally, two weeks later he was handed a $2,889.55 repair bill. The worst part was that the new compressor failed shortly after the warranty had ended. He said that he was limping around a bit after paying off that one......
The next time around with some help from the 928 sites, he did most of the leg work himself and replaced the needed components. After a professional evacuation/recharge of freon everything was blowing cold again. The total bill this time around was $478.....
Good Luck Manta, Michael
