I just bought a 1991 2.5 turbo mercedes so i can start burning biodesiel. It seems to be a great car despite it's 200k miles (it looks like new) - but the heater motor does not work. These Mercedes seem to be a very automated car - especially the heating system or climate control as the german engineers like to call it. Here's the symptoms:

1) the heater motor does not work under any conditions
2) the temperature control dial does not seem to have much effect on the small amount of air that comes out of the vents. It always seems to be warm even when the dial is turned to a low setting such as 60 degrees.

Would it be prudent to replace the heater fan motor (it I could find it) or should I be considering some problem with the control unit somewhere?

thanks in advance,

Dino