99 Jeep Wrangler TJ A/C not working?

I have a 99 Jeep Wrangler 2.5L 4 cyl. About a year ago the a/c went out. I have taken to a local repair shop and they said they tested for a leak and couldnt find one. They charged the system, and within 2 days it was only blowing hot air again. I was in the middle of a move and couldnt take it back. I was given a kit to charge the system by a friend, and when it is connected and filling, the dial on the meter will go up to full, and then I hear a clicking noise and then it says to keep filling. Any ideas on where to diagnose the problem?