yes the "off switch" should be function in case that I decided that I don't want my A/C I have a "choice" of switching it off. That's how it works on my W202 C36 but apparently not so in a W210 E200...

In a W202 if you turned the ignition OFF while the EC LED is on, it actually will restart with EC led on next time. Which means the A/C will stay off by default.

I find that a lot more intuitive and reasonable than a vent system that runs A/C 24/7 unless blower stops.

It's just really annoying. Also I cannot operate the vehicle when the A/C pump fails this way because 1 belt drives A/C, waterpump, alternator and power steering, if the A/C suddenly decides to completely seize in you end up with a real problem since the A/C clutch cannot be disengaged manually. I suppose when it does do that Mercedes expect you to drive the car to the dealer with no blower and suffocate in one of the most polluted cities on the planet.....Good grief.