The compressor is protected by the low pressure switch, if system pressure is low the compressor is not allowed to run. It sounds like the system was properly cleaned out and flushed, sucked down and held a vacuum (no leaks).If the condenser fan is running when you engage the a/c the electrical side of the system is somewhat alive.I know we had a Cadillac de Ville in the shop that one of the fellows had a lot of a/c problems with. There is a professional service called Identafix. http://www.identifix.com/info/about_us.htm They only deal with professional repair shops. They are in the Minnesota 651-633-8007 begin_of_the_skype_highlighting 651-633-8007 end_of_the_skype_highlighting. Your auto repair shop do all their diagnosis tests, and discuss your problem with a team of professional technicians great service cheap and very bright people. If the repair shop that are repairing your car are stumped this is a great service. This company only deal with automotive repair shops and don't answer questions for the general public but are an amazing knowledge base. This may be your best bet. If you are going to try to diagnose the problem yourself there is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online