Where ever you took the car to get the AC repaired should be responsible for fixing your car back to the same way you dropped if off. They probably damaged something in the car that's preventing it from starting. If its an AC job then you didnt have to do timing nor valve since they have no business messing with those parts for an AC job. There are many reasons why the car won’t start and you can start by getting the car diagnosed with a scanner. Could be a bad sensor like crank sensor or they caused a short in the car while working on the AC with battery still hooked up. Hopefully they did not short out your PCM.