Airconditioner causes overheating

Question: 1990 Lincoln Towncar, overheating on long trips (two marks)using the airconditioner. Without using air it does not heat up two marks and upon using the air will heat up and then the air will shut down . I have tighten up the belts, replaced thermastat, replaced fan clutch, checked water level and even replaced the airconditioner temperature switch. Help me with my problem, where do I go next. Ken

IMHO, it sounds like the compressor if too difficult to spin, causing un-due stress on the engine. I'm no AC guy, so that's just a suggestion :) (http://www.lincolnsonline.com/cgi-bin/ultimatebb.cgi?ubb=forum&f=3)

You could try those ^^^ guys ^^^ too.