blower motor only seems to run very slow low speed. wondering what "controls" the speeds as in a relay or something like what is on a w123, some kind of multi-resistor type box? Any one have an idea, I'm betting some one does!

Is this slow blower speed in AUTO? What are the results when HI or LO speed are selected?

On the W126, there is a blower speed controller.

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Sam

84 300SD 350K+ miles ( Blue Belle )

There is a blower speed controller that determines which resistors to put in series with the blower.

From 1986, 126s have a solid state blower controller also called the porcupine.

Sixto
87 300D

Thanks for the response, guys.

SD Blue, the low, slow speed is all the time, makes no difference, Auto, Low or High selections.

Sixto, this is a 1983 vintage model w126 300sd so I'm very interested in finding out all about the blower speed controller and the resistors of which you write. Such as where the blower speed controller is located and are those resistors in that unit? Maybe some ohming values across which terminals? Maybe some pic's or point me in the direction of another thread that address these issues.

Tia for all the help!

there are 2 large relays left and right of the blower motor enclosure...i think the silver one on the right is the "Geblaeseregler (speed regulator)...might be worth checking out...sorry i have no info on how to test it

Hmmm.............I just got back home to my schematics. The first, and most obvious, factor is fuse F11, which powers the blower motor controller. This I'm not sure of, but if the controller doesn't have power, it may "default" to the low speed setting. Don't hold me to this as it is a stab in the dark.

Another factor might be the blower motor itself. Have you tried unplugging it and applying +12Vdc directly? If it is about worn out, it may be drawing too much current. Mine started hanging up and needed a "bump" start. Even then, it was pretty sluggish. I tried just replacing the brushes but it didn't last long and ended with finally replacing the motor.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I appreciate all the tips and insights everyone is offering. I'm going to look at all these ideas...just as soon as my son lets the wheels stop rolling long enough! All these points really sound good and I'm going to pull the motor out, put a straight 12v to it, see what it does with an amp meter hooked up, also take ya'll up on the tips on how to replace the brushes while I'm at it. I've also gotten that fuse upgrade kit from MB to install. It doesn't come with any instructions so I'll see what I can see about doing that too. I'll let ya'll know how it goes asap. Any more ideas and tips, keep 'em coming