you need to remove the wire plug from the low pressure switch on the AC system. you then jump it with a piece of wire with the car running and the climate control in the on position. watch and listen for the compressor to come on when you just the wires. dont let it run long, this will tell you that there is either low freon OR a bad pressure switch, both easy fixes. for the location of the switch, I cannot help you.

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Matt
2003 Jetta Wagon TDI 145,000MI
1999.5 Jetta TDI 287,000MI
2001 Suzuki SV650S 26,000MI
2008 Yamaha Vino 125 11,000MI
http://www.crazymatt.org