My SD just did this too and to cure the problem, I did two things. Pull blower motor and replace brushes -believe me, if your car has some miles on it, they all need new brushes, easy! More importantly and this is a known w126 issue, bypass fuse block (fuse for blower) and replace with a 30 amp strip fuse as too much resistance has built up in your system over the years. Many cars have already had this done and many more have not. Go to a PNP and find a remote fuse block out of any 126 car (mounted on firewall close to brake master) remove and wire to your car, took me 30 minutes and voila, instant blower again in my '82 300sd -you will be happy you did this! Good luck!