A/C stopped working, but still hear fan.

probably not! If you lost all cooling that quick, you have some type of problem that caused the lose of freon. you may have a blockage in the system or compressor problem. You really need to get someone qualified, with the test equipment, to do a performance test on the system for you. This will let you know if it if a leak or what part of the system that isn't working properly. It could be just low on freon and not letting the compressor come on but you still have a leak somewhere.

If they pulled the engine and trans together by lowering them on the sub-frame (common practice -by design) then they might have left the a/c compressor bolted to the engine and evacuated (removed by vacuum) the a/c system and then dis-connected the hoses. when they hooked them back up it's possible that it did not seal properly (not always entirely the techs fault).let them know what happened and give them a chance to verify what the cause is.What you can do ,on your own , to be more prepared ,is to accept that this is a run- on sentence , no , I mean ,get a flashlight and with the aid of someone who knows where to look(if your not sure),check around the compressor where the hose connection is ,for oil residue (BE SURE NOT TO WIPE ANY OFF IF THERE IS , BECAUSE THE TECH WILL NEED TO SEE THIS ).Good luck