I replaced a fan clutch on my BMW just last month and I haven't done it on a Mercedes. But this is how I did it on my BMW. I used a 32 mm metric wrench (was specified in the BMW repair manual) and fit that on the clutch bolt. Took a hammer and tapped it semihard in CLOCKWISE direction and it loosened. I don't know for some reason atleast on BMWs, you have to unscrew it in CLOCKWISE direction. Installing it is the reverse and whole thing took me 30 minutes to do on my BMW. Hope this helps.
92 190E 2.6, 97kmiles
86 BMW 325E, 136K miles