I think you are supposed to remove the schrader valve before you install the r-134a quick-disconnect fitting. That's what I did when I converted one of my Mercedes. One alternative is to use a tool that allows you to change the schrader (r-12) valve without evacuating the system. You see them for sale on ebay occassionally for around $45-$50. I bought one on ebay because I also had a bad schrader valve, but have since sold my car with r-12. I was going to resell it on ebay, but if you would like the tool I'll sell it to you for $40. It was only used once, and its a lot easier and cheaper than paying someone to evacuate the a/c and do the repair.

FYI, evacuating the refrigerant takes oil out of the system as well. A good a/c mechanic will measure the amount of oil that came out (via the oil-trap in the evacuating machine) and put that much back in when they charge the system. Good luck finding someone who will do the job that thoroughly.

Let me know. gregory_spring@hotmail.com.

GregS