I have a '98 E300, which I think has the same fan clutch as your car. I recently put a new one in.

When the motor of my car is not running. the motor is cold, and I face the car from the front, I can turn the fan clockwise with my finger but there is some resistance and the fan stops immediately when I take my finger from the fan blade. The fan definitely does not spin. I think that is what is supposed to if the fan clutch is working properly. (I have not tried to turn the fan counterclockwise.)

When the motor is cold and running, you should be able to stop the fan from the driver's side with a rolled up section of a newspaper as the clutch has not yet engaged.