If you got colder air at some point then I'll hazard a guess and say your compressor runs.... however, look on the left side of the engine. half way down for something that looks like
the whole face should be spinning around if your system is atleast attempting to work when you turn it on. otherwise, the belt will ride around it and the center part on the front wont move at all.
you said you added R134a to the system and it got colder.... you should have seen if there was a charge in the system first, and if there was how much was there... over charging systems is not good... That being said, you most likely have a leak in the system if it got cold, then warmed up again. Common fail points for the 124's is the AC part in the Dash Evaporator I think it is. the dash has to come out to do that. while it sounds daunting it can be a DIY. More information will help, How long have you had the car, is this a recent issue, did your system get cooler then heat up again or did it stay 'cooler'?