Mercedes: heat, no blower, rotary switch, temp control

Question
I have a 1978 450 slc, the heat comes on but no blower, and the switch seems not to work and the temp control rotary switch does nothing either. I have good fuses  so I am left scratching my head
Help, thanks

Answer
Dennis,
I am having the same issue with my blower on a 1986 420SEL. My research indicates that is it the blower control unit. This is inside the blower no my car. Requires dropping the carpet, and the panels under the passenger side dash. I have located a used part and hope this will solve the problem.
Good Luck
Rob