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Old 09-22-2009, 11:42 PM
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Join Date: Sep 2009
Posts: 11
Exclamation Blower Electrical Woes - 91 300D W124

My blower fan has me stumped. I converted the o-rings, drier, and expansion valve for an r134a conversion, everything went fine, except the fan suddenly did not work after it was all said and done.

I did the required reading, figured it was a regulator problem and ordered a new one. This new one behaves exactly like the other one in that the fan doesn't work.

The fan has voltage all the way to it from the posts behind the brake booster. At those posts, one is ground (very solid and tested), one is +12v, and the other is yellow and switches with the desired fan speed at like 2.8v and 9v (and 0v). The blue wire coming out of the fan regulator (big heatsink lookin fella) has no obvious charge, nor does it change to complete a circuit around the blower fan.

The blower works benchtested. You hook it up to the battery and it goes. If you ground the blue-wire out, the fan goes.

I stopped by the local parts store and picked up a number of fuses to replace some of the badly corroded ones, and then a heavy duty 30amp fuse to replace the stripfuse, outside the fusebox.

These fuse changes affected nothing as far as the blower goes.

Any ideas? Is KLIMA+Kickdown involved with allowing the fan to run at all? I pulled this unit out to get to the OVP and replace a fuse. I've pulled it out and reseated it and it didn't change anything.

I've got a trip coming up on Thursday and would have been done already if this newest gremlin hadn't popped up. Any help you guys can offer would be much appreciated! I've read through most everything relevant on the board so far and can't find anything definitive, other than the regulator. What're the chances that the one that I bought doesn't work for the same reason as my original?

-A humble newbie.
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Old 09-22-2009, 11:58 PM
oso oso is offline
'87 300TD
Join Date: Oct 2007
Location: San Antonio, TX
Posts: 189
A week ago I finally made it to the blower motor that suddennly stopped working mid-trip.Beforehand I tested the system couple more times, replaced the fuse, made sure juice was on and nothing. Took the motor out, connected to the battery and it ran no problem! Put it back into the cage without touching a thing and it worked again! After cleanning everything around it I put everything back together and so far so good....
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Old 09-23-2009, 12:46 AM
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Join Date: Sep 2009
Posts: 11
Is it possible that the electrical system doesn't let it run with the wiper unplugged? All of my testing has been with the blower out of the car, or snapped into its enclosure. Maybe it wants everything to be whole before it runs?

I can give that a try I guess. I can't say I haven't thought about putting it all back together and just hoping that it works when I'm done..
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Old 09-23-2009, 01:06 AM
oso oso is offline
'87 300TD
Join Date: Oct 2007
Location: San Antonio, TX
Posts: 189
Have you checked for the voltage on the 2 wires that power the motor? Do you have the juice there when the blower is switched on?
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Old 09-23-2009, 01:32 AM
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Join Date: Sep 2009
Posts: 11
The red wire from the controller is always +12v hot. From the post opposite of red wire, that is also hot.

Nothing's getting through the blue wire. Could it be a faulty ground somewhere? I'd have to cut the wiring or do some digging on the plug to test that past the post.

When it's not running, there's also no current going through the 30amp fuse positioned just in front of the main fusebox. Both sides have power, but nothing down the line is using it. I was under the impression that this fuse was for the blower fan only. I haven't seen the wiring up close that runs to/from that fuse back inbetween the double firewall.

The fan tested fine when 12v was applied, and I have a receipt from the PO that shows a used one was put in at some point in the past 6 months. Maybe it too has just gone bad? I hate to think about that, but it's possible.
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Old 09-23-2009, 12:35 PM
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Join Date: Sep 2009
Posts: 11

I've been thinking about this problem a little more and while I still hold out hope that a solution exists, I have to plan for contingencies. I just bought this car and to have the ACC fan be the only thing preventing me from taking it on a trip is unacceptable to me.

Issue #1 that stands out to me is the battery. Mine is currently nearly dead, which I plan to rectify.

2: what're the chances that the ground post to the fan regulator works for my simple voltmeter but not for the regulator? I'm tempted to splice in a solid ground connection on the regulator plug wiring, just in case.

3: brushes? If these are bad I'll likely just order a new fan. This issue shouldn't affect the voltage problems on the fan side of the regulator, however.

Right now my temporarily solution is going to be a switch of some kind to power the fan so I can use it if I need it, but that is far from ideal.

Are there any wires/connectors/vacuum lines around the area of the expansion valve that aren't readily visible that could be affecting my problem? I've looked down there, as well as the wiring diagram and can't find a anything.

As usual, any help is appreciated!

Thank you!
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Old 09-23-2009, 12:55 PM
babymog's Avatar
Loose Cannon - No Balls
Join Date: Jan 2006
Location: Northeast Indiana
Posts: 10,767
Always test for voltage and ground with a test light, a meter can show voltage where there's no current available.

Gone to the dark side

- Jeff
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