Could the blower switch be a resistor switch?
I know a number of cars have resistor switches and when the resistor goes south the blower may only work on one setting, if it works at all. I'm not sure which Mercedes models use the resistor switches though.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.