Hello Mark,
Thank you very much for your answer too.
Pontiac published a stand-along ATC servicing and repairing guide - I think it is pretty much a repeat of what is in the Pontiac AC service manual but perhaps with some updated diagnostic testing procedures. If you send me a PM with your email address I will send you a pdf of it.
Thank you very much for your offer, I will do that and send a PM.
I also received a document from Paul that is very professional and also helps a lot.
I ordered a transducer from CaddyDaddy. He thinks this will also work on a Pontiac.
The transducer will be delivered in two weeks. I'll let you know if it works.
Many greetings,
Joerg