bought a new climiate control fan motor with blades. Have power to the motor but it will not start. Need advise, must be missing something. Desperate for AC 1990 Mercedes 300E

Ground the blu wire and see if it starts..

Thanks Arthur, yes that got the fan motor running. Fan speed control system not working . Noticed that when old fan was hooked up, that both wire leads were hot. Anyway we have some fan action now. Will sort out more as time permits. Your the best Arthur.

OK..That was just a quick test for regulator circuit and motor verification..
Now , the yellow wire at the regulator is a variable voltage [ 2-7v] that triggers the regulator. Put the Defroster On high and see if you have voltage at the yl wire and ground.
This can also be done right behind the brake booster..there is a 3 wire plug that comes from the CC..
[ red/yl/blk]...you should have 12v from red to blk, and variable voltage from yl to blk.
If you do , then the regulator is bad ..is you don't , we have to continue w/other test.
Basically , when the reg gets trigger voltage [ yl wire] from the CC, it grounds the blu wire thru the regulator. It is a Switched Ground, but variable. The red on blower is always HOT and have nothing to do with speed regulation..that is done on th ground side of fan motor [ blu]....which is why I had you ground that blu wire ..that test by-passes the reg/CC circuits and brings on High Fan w/o regulator/CC in the circuit..

Three wire box behind P.S. Booster.Black yellow red. Defroster button pushed. Fan blowing.Black wire 0. Red wire 12v. Yellow maybe I'm thinking 4v. Ground wire to make fan operate still hooked up at test time. Are you thinking that the speed regulator is kaput? Still in working world so takes a while to get all tests conducted. Also might add fan blowing with much effort but not much air blowing inside. By the sound of it , it should be having more force inside car. First time the fan was started ,mounted in bracket, and no shrouds on lots of force blowing up toward hood. Did I say lots of force? oh boy. What are chances that the fin direction is wrong? Seems to be oriented like the old one was.

I seem to remember that there was a lot of air blowing straight upwards when I replaced my blower motor not too long ago. Don't forget that you have the cover going back on top of that motor still. When my car runs (long story) there's plenty of air coming out all vents on all sides, so I wouldn't worry about it.

The blower motor regulators don't last much longer than the blower motors themselves, and it's not much more work to get the regulator out (it should be just beneath the plastic support for the motor). Replacing both at the same time might not be a bad idea.

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Steven Harrison

1993 300E2.8 - 196K
2001 E320 4MATIC - 86K

appreciate the help Stephen. Good advice on the speed control. Don't think were happy with fan at full speed. Now , I should say that the new fan motor is somewhat different than the old, and required a different bracket and hold down. Don't remember seeing this control but will look again. Is the speed control change pretty straighforward? Out with the old in with the new? Any one that can give a specific direction, or how to please advise further. and thanks.

I believe there was a change in manufacturers for the blower motors. I remember reading somewhere (possibly on repair sheet 83-556) that Behr motors were used up to 1998 and Siemens units afterwards, but only Behr units are available now.

The two may have different mounting brackets, which might be what you're seeing.

The blower motor regulator lives directly under a black plastic cover that the blower motor mounting bracket sits on. If I remember correctly, I didn't have to (or couldn't) completely remove the cover, but unscrewing it from one end and some careful twisting and pulling of the regulator from either side got the old regulator out.

The regulator is attached to a large aluminium heatsink, it's roughly triangular in shape. I have my old one somewhere, might be able to send a picture if you need one.

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Steven Harrison

1993 300E2.8 - 196K
2001 E320 4MATIC - 86K

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