Murphys Law and W124 freon escape
 

93 300 Cabrio. Went to add refrigerant. Low side fittting and valve cover OK. High side - bigger plastic cap, on there pretty good. A twist with some pliers and it came off, and valve below began to hiss. This is bad, so put cap back on. Crank car, and pressure blows cap off into the bushes. Look at cap and realize it must have been from the R12-R134a conversion program, it was glued in place by something like green Locktite.

As I stood there, listening to my refrigerant vent, I recalled that it was expected to be 95-96 today.

So is this conversion an adapter that is screwed into the original valve? What do I ask for at the parts counter or look for at the boneyard? I have my own vac pump and gauges.

you can buy R12-R134 adapters from spares shops - some junkyard cars which had this conversion would have them too.

Most box stores have these on the shelves to. NAPA is best if you have one.

Are you assuming it was converted r12 to 134a, or do you know for sure. Look for the refrigerant ID sticker on the bodywork next to the radiator.