I had the AC in my truck go in spectacular fashion 2 summers ago. Yes, that hoopty used to have ice cold ac believe it or not!!!
In a parking lot jump in and fire it up. Crank on the AC and white smoke just POURS out the fenders and grill and hood scoop! Flat out looked on fire! I shut it of and jump out. At this point I notice a fire truck is already parked behind me and a fire fighter is walking up already. It's been seriously 10-15 seconds at most. I'm thinking damn, this is service!!! He asks if everything is okay and I tell him I'm not sure. Pop the hood and more smoke pours out. Once it clears it's a mystery... Can't find any sign of it. I fire it back up and the excitement is done. I send the firefighter on his way. I turn on the ac and it's hot. OHHHHHHHHHHHHHHHHHHH Pop the hood and look for oily stuff and finally I find a fitting that let loose. Later that year I did an engine swap and did away with heater and ac altogether. LOL
But like they said, look to see if the clutch is spinning. If so, probably lost an oring or leak or something. Unless it's actually pushing out hot air. If that's the case it's possibly just the control box or selector dealio.