if you have a r-12 system, its got bicyle type shrader valves to connect to, they even have threads, r134a has a distinct connection type, its a quick coupling with like a red and blue cap, sometimes black. its big around as a small finger or your pinkie with a ring around a quater inch below the orifice of the valve. also look for 134a sticker under hood. if the valves are screwed on, do not fill full, leave it at around 80-8 percent full, do the math, i think you may have a 2.5 # system.look for the l on the pump and follow it to the valve, this is where you charge it. if you have no s/d markings, its the big pipe.