Fan has been working great. Then today it would not come on. Figured fuse or such, but then it popped back on and was fully controllable. After I started up the car again later, no go and been dead since.

I am asking if vacuum control has anything to do with it because I noticed my idle went way up and I could hear hissing. So when I got home I found that the rubber intake tube under the fuel dist. was collapsed and cracked bad. Its new and its URO. Figures, eh?

Both of these happened today. Related by chance? If not I need to order more than just a replacement rubber tube ASAP.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Fan not related to vacuum. Could be the ccu, the fan speed resistor, or fan brushes. If you can get to the fan cage see if it will run when you give it a push start with your finger (ccu on defrost and key on). If so then brushes probably bad. If you have a voltmeter you can check voltage going to the fan also.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K

You've ruled out the 30 Amp strip fuse? I'd sure want to inspect that before tearing into the blower housing and fooling with the fan motor.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Ya. Fuse was fine. Even replaced it. In fact, when I turn the system on I do hear a very, very faint motor sound (or something) and air moves at an incredibly slow rate. Pressing different buttons does also changed the output locations, so that much works fine. Where is the fan speed resistor?

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Check fuse again. Good. And there is lots on that fuse, like back-up lights. Those work fine.

From what I can tell the fan is running very, very slowly. At idle there is air flow out of the vents. Nice and warm (as it should be). When off, airflow stops. Or on defrost, air out by window. Its just not much.

So it seems its stuck on super slow mode. But today it kicked in again for a while, but this time crawled to slow mode after 10 minutes or so.

Any ideas? If the blower motor easy to get to? I could try 12 volts right at it.

edit: Searched and found how easy the fan is to get to!

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

i am having a similar problem and like to know how you have progressed.
thanks
mak
300se

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mark

Well while I should have been working on this issues, I swapped some fog stuff around from US to Euro. So I will be working on this tomorrow.

I am guessing that its the regulator thing near the motor. Some describe it as "porcupine like" - I think they are heat sink "needles". Also found that new they cost a small fortune.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Your car has a W124 climate control system, which has built in short detection on the control module: If it finds a short it either shuts off the item with a short or shuts down the whole system... depending on the version (I don't recall what a 91 would have).

The spikey looking thing is the voltage regulator for the blower motor. As I recall the control unit sends a 0-5v signal to it, and it spits out the 0-12v power for the blower motor.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Well the fan like sound I heard are several small fans I found in the dash. NO clue what they are for. The one on the passenger side comes on with key, even with HVAC off. With HVAC on and blower fan off I can still hear a fan come on in the center of the dash. Must be some small back-up fan? I get airflow as I mentioned, just not much. But now I know that airflow is NOT the main fan.

Re-soldered the voltage regulator connections and cleaned ones at the motor. No help. I have not tried 12v at blower itself yet.

But I did test the leads to the blower once removed. 0 voltage at all positions. So then I jumped the 7.14v I was getting at the regulator. Verified at the motor leads and hooked up. Nothing. In high mode I was getting 7.14 volt at a few positions from red. Red to yellow and red to black I think.

Cant find any wire. But I jumping that 7 volt and nothing. So not sure at this point was could be going on. Maybe the blower motor took out the regulator.

Also again today it was blowing full blast again for a while then cut out. So its still intermittent. I hate issues like this.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Well since I am new to the whole Euro stuff I assumed that by strip fuse you meant the fuse. After all, they are a thin strip of metal.

No one specifically mentioned one outside the fuse box!

After some searching old threads I found what a strip fuse really was. Then I found one for the blower. Its on the back side of the false firewall. In front of the master cylinder. Looks like a cable connection, but the cover hinges open and there was a thin metal strip. It was pretty corroded and had a small crack. Lifted it up a little in the middle and it was in two. Going to make one out of a soda can for now. If I had known about these weird "strip fuses" I would have checked.

So at this point I had taken the blower out. Not hard and good learning. Also noted I need new brushes ASAP! So not all is lost there. But I ALSO too out the HVAC controls and re-soldered them! With my aftermarket head unit, it was a pain and will be a pain to put back together!

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car