2004 ML500- Twice this past winter (on extremely cold days) the heater/AC blower motor cut off randomly. I tested the fan directly and it worked fine so I ordered a new resistor/regulator to put in it (because of age I ordered a blower motor as well).
While waiting on the parts it began working fine again and I figured I would do the job when it went out again. It has been fine until the past few weeks (extremely hot days). It randomly shut off a few times in the past couple weeks and finally stopped all
together a few days ago. Having the fan and resistor in the garage, I started my diagnostics over again from scratch. Fan again worked fine on direct 12v power source. I went ahead and unplugged the pigtails from the old resistor and just plugged in the new
one before I uninstalled/installed and fan still did not run (even on highest speed). I checked the voltage coming out of the resistor to the motor and it was around 3.5v so I checked the red wire(?) going into the resistor and it was always about the same
as the exiting voltage. Even though it was getting a little power I checked the fuse under passenger side by the blower and of course it was fine. I went to the relay under the hood and swapped it with a good one and nothing changed. I pulled the relay and
tested the socket pins and the pin from the fan switch tested no power when off and full power at the pin when I turned the fan switch on. I have not pulled the climate control
panel because I can't pull the radio yet (read that was step 1). The rear climate
control is working fine. When I have it on auto (controlled with front) it changes with all fan speed settings and off. When I change temp setting on front auto it gets faster the colder I set it and slower the warmer I set it and off when I exceed current
ambient temp. This is all this DIYer knows to do. With all this being said I know the question is ..... why 3.5 v and am I done until I can pull the climate panel? I don't have a schematic and I am having a hard time finding continuity consistently.