Hello satyr,

No answers untill now?
I am living in Europ and own and drive a W 124.193. That meens a wagon with a 603 - 3.0 l turbo Diesel.
It is equiped with a manual airco to. I don't know the working of your system but mine is adjusted by two wheels. One for the right side and one for the left. To engage the compressor, I have to turn one of the wheels to maximum cold. Just before the stop I can feel/hear a switch clicking. Choosing a temp higher will only engage the comp in function of the requested temp/outside temp. I am wondering if you can hear that click to when sliding your selector?
A good friend of mine is my indy and a very competent independant MB specialist especially for older MB's.
If you want I will ask hem for a wiring diagram (if he has one).
Beware : a cycling AC compressor meens there is not enough refrigerant in the system! There are tons of information on this forum about this toppic so did you do a search? That would at least partly answer some of your questions.
As my indy don't speak/read or write any English, I will act as your inbetween if necesarry. Just let me know.
Good luck!

Danny