a/c charged but hot air blowing within a week

I had my a/c charged and oil added and it was blowing cold. within the week (and halfway through a ten hour away trip) it had gone slowly from cold to hot air blowing. should I just get a/c system replaced or is it just a leak? I hate to waste money to see if it's a leak and then find out it's the compressor. I can't do another summer of the a/c being out in the truck