1996 GMC Jimmy

Air Conditioning problem
1996 GMC Jimmy 6 cyl All Wheel Drive Automatic

I recently just bought this jimmy and the air conditioner didnt seem to work.I thought maybe it was out of freeon and needed to be recharged. So I recharged it with the R134A coolant that you can buy at walmart and that didnt seem to work when the guage said it was full.A couple of days later it said it was low again and so I recharged it again and the compressor turned on this time but it will not stay on and it still does not blow out cold air. Any suggestions on what to do. The compressor just turns on and turns back off on its own.