So, then there are actually TWO shrader valves, one on top of the other?
No. Either you remove the one in the R12 fitting before you put on an R134a fitting that has its own, or the R134a fitting has an extension to push the button on the R12's valve. The latter is a pita because when/if the valve needs servicing you can't get to it.
I just take 'em off, blow/dump out as much of the evil oil-like substance they've put in it, put in new R12 oil and recharge with secret sauce. I've done that once, on my wife's 560 SL. We'll see how it holds up. (I used gasoline to sluice out the compressor when I had it off for servicing.) This summer will be its first real endurance test, though it has sat and held a charge for nearly two years. -- Jim
