Blower high speed not working

What is the most common cause of the blower not working in high speed only. How difficult is this to fix? Thanks in advance.

[RG5384]

i dont know any fix or anyting about it, but it may help if you put the yr/model car your talking about.
R

[Jim Anderson]

On my 190e the blower comes on when the super defrost is on (with the AC.) The blower high speed is probably wired through that switch, that could could be your problem. Does your super defrost work, if you have it?

It's an '83 300 sd. Sorry for not including the info.

[Breckman99]

I had this exact problem on my 80 300SD and let it go until the blower finally stopped. I removed the motor and ground out the compression clamps to remove the back bearing plate and discovered the brushes were completely worn down. You can go to a parts supply store for new brushes - I used some out of a Hoover vacuum that I had laying around and they worked fine with a small amount of modification. When you put the bearing plate back on make sure it is properly aligned and tack weld it back on. Before you go ripping into the motor check the power supply circuits and all contacts to make sure that isn’t the problem!

Thanks for that advice!:p

[RG5384]

does your derfrost work? if so then it's not your motor, as the defrost uses the motors full speed. How high will the fan speed go on automatic? I have a funny feeling you have a cold solder joint on your "high" switch. Same thing comes and goes on my 300SD, i'll fix it someday.
Ryan