Ford Repair: Air conditioning question, r 134 freon, compressor clutch

Question
I have a 99 Mustang GT that has always had air conditioning problems. The air would work fine and then start blowing warm and after awhile it would start working again. It was at the dealer several times under warranty. They witnessed the problem but could never fix it. No error codes are produced. They gave me the car back for the labor day weekend of 2004 and said to bring it back whenever I could and they would have at it again. It worked perfectly until the other day. Of course the extended warranty is long gone. It does nothing but blow warm air and I noticed the compressor clutch is not engaged and not spinning. I have a code reader and there are no codes. When the air switch is on the motor slightly revs every few seconds. What do you think?   Thanks Mark

Answer
You may be low on R-134 freon, and the compressor is short-cycling. Ford had a lot of problems with the compressor seals leaking, sometimes even the compressor itself. Yours' has a tracer dye in it, see if you can get a blacklight or have a shop check it signs of the dye leaking. They might try to sell you a service including dye, you don't need dye added since Ford started putting dye in at the factory around 1993.