Okay...how does this freaking vacuum system work? (in simple terms!) I am familiar with the VW/Audi system..which is controlled by a vacuum pump in the trunk...however I am getting mixed information on the MB system..maybe because it varies with each year? Here is a rundown of my car....

The Power locks, trunk, and fuel door actuators are not working (the fuel door is unlocked, and the trunk I can open with a key). The cruise control also does not work. Now, everything else on the car works fine...transmission shifts fine...car turns off fine....(both of which I was told ran on the same vacuum system) Would or should I hear anything when I use the locks? I hear nothing...no pump, no hissing..nothing....
The car is currently at the body shop getting body work done....but would like to get feed back on other users' history/remedies.

Thanks!!! Other than that, I LOVE this car!!!!!!!