Last year the a/c worked great, this year.....nothing. Any guidance on where to start. Thanks.
If the compressor doesn't come on, it could be electrical (a tripped circut breaker or blown fuse), or the system might be low enough on refrigerant, that the pressure switch won't allow the compressor to come on.
The system was originally R12. If the fittings on the compressor are threaded, than it should still be R12. If the fittings don't have thread, than it has probably been retro-fitted to R134. You don't want to mix the gasses. You would fill it on the suction side of the system. Look at the two hoses that connect to the compressor. The larger diameter one is the suction side (it comes from the firewall (evaporator) up to the compressor. It will be the side closest to the engine-marked "S". Adjacent to the connection at the compressor is the fitting that you fill the system thru.