406 Estate - What I did to solve blower motor speed control not working

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joydivision
Donor 2021
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Joined: 20 Jun 2021, 11:31
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406 Estate - What I did to solve blower motor speed control not working

Post by joydivision »

I recently fixed the blower motor speed control on my 406 Estate 2.1TD. It would only work at max speed setting, all other steps the motor wouldn't even turn on. All first research I did pointed into direction of the blower motor speed control module (which in this model is fixed to the motor itself, it's the "half moon" two-transistor thingie which can be found in many different versions on the internet, as I found out later, and was used in many french cars...). BUT: it was NOT the culprit here. I will tell first what exactly was the problem and what solved it, and then I will share some important info about the speed control module.

The problem was: someone had changed the blower motor to a motor from a Citroen Xantia (I think), and a small brown wire with a black connector was left UNCONNECTED. Why? Because the Xantia motor (a Valeo part) didn't come with that connector... but the head unit of this 406 needs that wire to enable the PWM control to pulse the GND by means of the power transistors in that speed control module and like this regulate the speed.
I found this out by instinct, after having tried all other possibilities (and couldn't find anything wrong with motor or speed control module), as I had researched the motor, looking on the internet for photos from used motors, because I was suspecting that it was a connection problem (but I was always focussed on the 4 pin connector... that was well connected...), so I happened to notice that small black connector and mistakenly though it would only be some "additional ground". But then, when I had lost hours and already got TWO wrong new modules from part store (although they accepted one back, and tomorrow I will try to give back the second one...), I noticed a black connector from a brown wire in my car, which reminded me of the connector I had seen on the photos on the internet... measured it against the other control wires and bingo, it proved to be related (resistance in the kiloohm range), then made sure it wasn't live and then connected it just as it could be seen on the photos (to black wire coming from motor coil) and YES! Was working!

But wait, I have to tell the whole story and post images.

My 406 has this head unit:
s-l1600.jpg
The blower motor, although it is from a Xantia, is almost exactly the same as it would be if it was the right part, EXCEPT for the little black connector.
Unfortunately I forgot to take a photo of the blower motor.

But here's a photo of the motor I SHOULD have:
bower motor 406.jpg
On this pic it's not clear, but the black connector with the small gauged wire is connected to the thick black ground wire for the motor winding, so it basically carries the pulsed ground back to head unit for feedback... That's probably for safety - If that feedback is not present, the motor (or the power transistors on speed control module) has failed and the head unit won't send the PWM signal over the rosa control wire. I was unable, btw, to find out what the orange control wire is for. But connections are exactly as on this image. Mine had all of them, EXCEPT for the black wire with black connector (which has it's counterpart in my car, but with a thin BROWN wire).

Now to the story: after researching on the net, I went to part store with documents of my car and asked for a new speed control module. They sold me a module that looks like this:
external-content.duckduckgo.com.png
external-content.duckduckgo.com.png (95.54 KiB) Viewed 15 times
Which is NOT for my car, it's for the later 406, the HDI, for example, they have a different blower motor wiring.

So, after taking it all out, first thing was to give the motor a good clean (and deoxit spray application and lubrification). Then I took out the speed control module, which was looking really bad. Gave it a clean and noticed a "apparently" bad spot around the area where there seems to be a little "spring" that makes contact against a little disc on the heat sink. It wasn't making good contact. Thinking it was bad (although the transistors were measuring fine) and not being able to find any badly connected wires (hadn't seen the black connector yet), I went to part store, returned the wrong module and got a module that at first sight looked fine, this one:
DSC_2975_.JPG
DSC_2976_.JPG
If you have a 406 and find this on the net, do NOT buy this module. It works "backwards" (has NPN instead of PNP transistors, which means it's inverted, it pulses +12V instead of GND, which does NOT work for these cars. Maybe for some Citroen. Not sure. Unfortunately, there are some other similar versions from other companies, which don't work, and then there are a few, including the Valeo part (which is what I have, photo below), which DO work. Here's a topic that covers this (only found the topic much too late): viewtopic.php?t=64495
DSC_2977_.JPG
Stupidly enough all them go under same OEM part number, 6441.78.

As you can see, the little spring on mine is gone... that was the unfortunate result of trying to "fix" it (yes, sometimes I also break things :D), as it was making bad contact to heat sink (turns out it goes against a small disc shaped thermistor). I think that might be what the orange wire senses. If thermistor burns out (or resistance gets high) due to overheating, the continuity to heat sink is lost. So I had officially "deactivated" my control module, without wanting to. That was too bad, as I had just found out that the new module I had bought was the wrong one, too, and that this old module seemed to work. I installed a resistor instead. Might not be the safest solution, as it might allow the transistors to die, but I'm going to be careful with blower motor, avoiding to run it at high speeds. And I never tested module outside of fan! it needs the fan running to cool down...
Btw, for testing, I never used the blower motor, I used a low power 12V mini drill motor. So, as soon as I had figured out that the black connector and small guaged wire was the problem (see photo of my test wiring for mini drill motor below), I connected it all together and speed control worked nicely!
DSC_2973_.JPG
I soldered the resistance in place, to make the module work again, installed it onto blower motor, installed blower motor into place, connected all wires, INCLUDING the infamous brown/black thin wire with black connectors (as I didn't have the counter part on the motor, I simply soldered it) and tested , bingo, blower motor was working on all speed steps, but with a strange unpredicted result: it was working backwards, building up vacuum, it was sucking the air FROM the car, not blowing it into it! It was wired backwards, internally, that is, between the control module and motor winding. That was really odd, so I had to get the motor out again, disconnect the black and red wires from motor and connect the other way round and install it back. Now it was finally working fine. I can't explain this last issue, as on photos on the internet, they all seem to be wired like I had, but this particular motor has to be wired the other way round!

Here's photos of the infamous black connector:
DSC_2974_.JPG
With cable soldered to it:
DSC_2978_.JPG
Sorry for the low quality and quantity of pics, but this was a really tiresome adventure, and when I had it done, it was late already, I forgot to take more and better pics.

Hope this might help someone in the future.