Are you aware of :

http://pages.prodigy.net/jforgione/MB_S500.html check item 18, It's something kind of similar to what I believe you are speaking of.

I did read your post and link about Ford Scorpio AC modifications. Sounded just like what I wish my W140 had. But , where on my 95 S420 is that thermister located. Likely way down in the bowels of the evaporator housing. Anyone know which wires (colors), where they come out, and where they go, and what relays (switching on-off the compressor) they control?

Good luck,
DanielW