Blower motor problems....
 

The blower motor on my 93 300sd started acting weird a while back. Sometimes you could control the speed with the control panel and other times not.Then it started pulsing high/lo and would eventually settle and blow on high only. The other day it quit altogether,it has came on a time or two but quit after a few seconds. I am pretty sure the motor is still good. I think it may be a relay or control module problem. Anyone have any suggestions or ideas? Where is the blower motor located,I looked behind the glove box,I seem to remember some of the earlier ones were in the center behind the controls.If it is the relay/control module where might it be?

The blower motor is on the engine bay side of the glove box, where older MBs have the battery. Disconnect the red and green vacuum hoses and remove the screws and clips holding the airbox lid to expose the blower. Follow the heavy gauge red and blue motor wires to the solid state controller. If you're handy with a VOM, you can check whether the voltage pulsing comes from the signal from the dash control unit or the blower controller.

Sixto
87 300D

Thanks,I will go out to the garage and check under the hood.

Found what I believe to be the problem,there is a black module type thing bolted to the top of the blower motor. There are 4 wires going into it,when I moved the wires around the motor would start and stop. I finally found a good position and it would continue to run. I am guessing that would be the solid state controller and it is in need of replacement.

Not a cheap part -

http://catalog.peachparts.com/ShopByVehicle.epc?q=1993-Mercedes--Benz-300sd-Climate--Control&yearid=1993%40%401993&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6211:ED|10000113:MBC|1511% 40%40300SD&catid=242213%40%40Climate+Control&subcatid=242297@@Blower+Regulator&mode=PD

Don't forget some heat sink grease for the aluminum base.

Sixto
87 300D

Enlarged to show detail
 

Ouch. not cheap is right.

What year did MB start using this in the W126?

I removed the fan assy on my '86 W126 from under the glove box are to clean of dirt/devris and then lube the bushings to extend its life.

Here is the offending part mentioned above. What years/models did this appear?
http://img.eautopartscatalog.com/hir...300&height=300

That's a W140 part. The W126 uses a similar device attached to a heat sink with posts. Often called a porcupine -

http://www.carpartsdiscount.com/auto/viewer/pictures/63808/1000/1/P/2C496E4/mercedes_560sel_behr_heater_fan_resistor_oem_126_820_53_10_1268205310.html

Similar price too :(

US W126s from 1986 use the solid state contoller but I don't know if it's the same part through 1991. Earlier W126s use a resistor pack.

Sixto
87 300D

Not cheap is right.Is there anyway around this like maybe a relay or something. Or possibly an older style reostat type blower motor resistor? I know it's probably wishful thinking right. Anybody know what all models use this? Thanks

Check the brushes for wear. Mine acted that way. Closing the door might start the blower working and a few miles later it would stop. Gave all the indications that the control circuits were at fault. I moved the straps on the brushes to allow contact and works fine now.