Thanks everyone for all the informations. I went onto this job thinking it would just be the brushes so this is quite fustrating.
this is for my W126. I will try to do as suggested and try to spin it while it is humming, and check the voltage through the line.
The fuse on this car was not upgraded and it still has the normal ceremic type fuse. Interesting how Mercedesdr describe how the heat would make the fuse act funky i did not think of this before. how hard is it to do this upgrade? does it involve taking apart the dash or fuse box?
i really only need this for defrosting the windshield since the A/C doesn't work anymore. if i get desperate maybe i will just hook a wire with a toggle switch for a defrosting fan?
will work on it tomorrow and report back.