1997 Mercedes benz E420 Blower Motor running at 1/2 speed

[alabbasi]

Recently my blower motor does not seem to be running at full speed. It seems as if that if there was a setting range of 1-10, it will only blow to a max of 4 /10 regardless of whether I set it to auto or try to manually increase the speed.

Is this a known issue with these cars? Any thoughts towards a solution would be gratefully appreciated.

[mbdoc]

The W210 as well as "most MB's after 1986 use an electronic regulator that controlls the ground of the motor.

That is the most common problem, 95%+

[alabbasi]

Thanks, I will check my vin to see if it if the new ones are compatible.

[Arthur Dalton]

The other possible is the fan motor could have dry bearings or worn brushes...there are two simple test I use ..one is to spin the motor and see if it is nice and free, the other is to simply ground the blue wire going from the motor to the regulator. That should give you high fan..if YES , motor is OK.. and reg is suspect....if still slow , brushes/bearings are worn.

The last possible is too low a trigger voltage at the yellow wire from CP to regulator. that is speed control input for the regulator, but as Doc says, most likely reg is done...they heat fatique themselves to death.

Try the other two test first. Specially the blu jumper to ground..that gets full
Bat V to motor and by-passes the Regulator circuit . So. it is a true motor only test, direct.
If you get the diagnosis down to reg , I wll post the trigger V test before you buy a reg cuz they are $$$$$$$$$
..and check the filters for air-flow restriction.