Question for you A/C experts
 

Is the expansion valve for an R12 system different from one designed for R134? If so, does anybody make one for the 124 model?

I think all you can find these days are expansion valves labeled R-134a. They look exactly like the R-12 ex. valve, just have a sticker on the side stating R-134a compatibility. My understanding is the newer valves work fine with R-12. I have an R-134a valve in my 124 with R-406a and it cools great. I'd worry more about getting all four connections to seal tightly than whether it's labelled R-12 or R-134a.

Yes, they are different. I couldn't tell if are looking for the R12 or R134 model, but and you can get the latter from a dealer or Mercedesshop for about $40.

I converted over to R134 and the compressor crashed. Put on new compressor and recharged with R134. New dryers on both ocassions. I am about to reinstall the ac after having the engine out and want to get it flushed and recharged. I've heard off debris "clogging" the valve and figured I might as well replace it while I'm at it. I also need to know if there is a 134 pressure switch for the auxillary fan. Mine never worked right after the conversion.