Recharging the AC problem?

My brother bought a can of freon from wal-mart and tried to recharge the ac on his car (2003 Cadillac CTS) and he followed the directions and now his A/C doesn't work at all and shoots out warm air and doesn't get cold. Did he mess up his A/C trying to do this himself? he has no idea what he is doing and I think he screwed up his A/C.