gmc truck ac inop

this vehicle is a 1992 gmc 2500 pickup truck, ac has never worked since i have had it, i have attempted to convert to r134 with a kit bought from auto parts store. pulled vacuum for 15 minutes, then started to charge system. ac compressor started to come on and cycle during charging process, but after about a pound went into system ac compressor shut down and ac light on eatc display panel started to flash. now, no ac compressor operation, and ac light flashes anytime ac is turned on.