OK, I found online what I was (sort of) looking for.
The monitoring that is taking place is actually for freon LEVEL or quantity. On some models, this has to be set to "inactive" due to a software problem, again IIRC this was right arounf MY 2000-2001, I am thinking if no other faults can be found that this might do it. I'd be sure to check the actual values of the different temp sensors first.
Here is a link to what I stumbled on:
http://forums.mercedesclub.org.uk/showpost.php?p=247445&postcount=9
Beware though, this post makes it sound like monitoring of the PRESSURES is not taking place and you are screwed if the system loses pressure, which is NOT the cas,e the compressor will still shut off if it needs to. This "quantity" measuring thing I don't think ever really served a real purpose than to cause techs headaches.