The blower on our 76 450SL went south. After looking at this site, I realize that it's a common problem.
I'm fortunate in that there is not 1 computer in this car, that made the fix a lot easier.
First, I removed the blower motor. The brushes were fine but the communtater looked glazed. A good shot of Electrosolve( Radio Shack }cleaned that right up--reinstalled.
Next, I removed the panel below the radio and removed the switch. On my car it is a 4 position rotary switch. The switch is open sided and you can easily see the contacts. Again I used Electrosolve, but just as extra insurance, I used some very fine sandpaper( glued a small strip to a very small razor knife blade)and cleaned the contacts. I checked the continuity with a meter and YAHOO. Reinstalled and the blower now works like new.
Hope this info can help someone else.
Terry