Ac clutch will not engage 1998 gmc sierra

sounds like low or no refridgerent in the system. start there. You can the cycle switch (low pressure switch on the side of the reciever dryer. the alumunium can on the left side of the engine in the back. You can also jump the two pins with a jumper wire and see if the compressure turns on then. Do not let it run for more than a min. you could burn up your compressor.

Good luck