I am in a bind tonight, and in a hurry. did not find anything with a quick search.

i have 9V to the heater blower. it does not run. Have tried 2 other blowers, no go. Aux water pump is running good, and VDC changes to 0 when tuned off.

Where to go, and what to do next.

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83 300SD Dark Silver Dark brown inside

Try putting 12 volts to all your blowers and see if they work then. Brushes wear out on the 123 and 116 blowers. I assume they also do on the 126.

Have you tried it with the button in the defrost mode?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

9V is kind of whimpy. I second trying to bench test the blower. If you need parts the Vancouver Junkyard has a '85 380SE. Monday is 1/2 off day.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

I will bench test them now.
Does the motor regulate speed with current or voltage?
Motor should turn with 9V?

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83 300SD Dark Silver Dark brown inside

It should turn.

It regulates speed by running through those 'toaster wire' resistors which lower voltage. I think they are mounted between the firewalls in the SD. Now that I think about it 9V you were seeing may have just been a lower fan speed.

you can replace the brushes following this procedure (slightly modified for the W126): http://www.peachparts.com/Wikka/W123BlowerBrush

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Thanks for the info.
Found that the little black box next to the fan was bad.
Now I will not freeze tomorrow, unless something else breaks...

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83 300SD Dark Silver Dark brown inside

How did you figure that out? I assume you refer to the amplifier. I ask because if the fan was getting 9v at certain push button settings I believe it indicates the amplifier is working correctly. Also, when these motors start going bad, they become intermittent.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I figured it out by swaping the part. I have the (RIP) parts car. I had tried 3 blowers, and had no way to read amps. So I decided it had to be a current issue. Still do not understand how it all works together. But swapped that little box, and fan roared to life. Was not expecting it, was really frustrated, bout scare the SH#$ out of me! at 10PM in the cold

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83 300SD Dark Silver Dark brown inside

Nothing more startling than having something work when you're not expecting it to. I'm guessing from Kerry's post that the intermittent nature of the blower fan in my 83 sd could well be the motor giving up. I was kinda thinking it was just a bad connection somewhere that I would have to track down in the summer, when I don't need the heat.