J126 Fan controller

GuruX

A2OC Donor
A lot of threads are here about a hunting or breathing cabin fan. This is caused by the J126 controller going bad. As usual with electrics, it's just a matter of solder joints gone bad. This can be confirmed by removing the glove box, set your fan to a speed that doesn't work properly and then press the connector block to the controller with your finger. The fan rpm should vary with the pressure of your finger.

To find the J126 fan speed controller (in Swedish it's usually known as a heater fan resistor), follow the cable from your cabin fan, away from the fan. The first thing it connects to is the fan controller.

This part is removed by first removing the cabin fan, then the controller which is held on by a single screw. The controller isn't meant to be repaired, the circuit board is covered with a black rubbery paste. The paste can't be removed easily. But hey, someone put this together, I must be able to take it apart.

What you'll need are small torx bits. I think they might be TH6 and TH10. I managed however with a single TH8, and some luck. What you really need to know, is the location of the screws holding the circuit board. I couldn't find all of them, and broke my unit, but I'm sure I could have repaired it if I didn't break it during disassembly.

J126-screw-locations.jpg

As you can see. There are seven screws. Two of them, holding the connector block, can be seen without removing the black stuff. Three of them in the edges hold the transistors, and two of them hold the circuit bord.

I would find them all, remove them and then use an exacto knife to cut along the edges of the unit. There is a gap between the housing the circuit board on the long sides. This gap is about 1,5 mm, so be careful. You should get the circuit board and the connector block out in one piece. On the underside of the circuit board, you'll probably find cracked solder joints, resolder and then reassemble in reverse. Perhaps you should also restore some of that black muck, to protect the circuit board from condensation.

Good luck!
 
This would seam the problem we have.

Whilst checking the forum for our problem i came across this thread which seams to describe what's happening to our car. Ever since we bought it the interior fan speed even on it's full setting seamed a much lower speed than it should be. I've been out in the car on several occasions and very occaisionally you can go over a bump in the road and the fan speed will suddenly and momentarily increase to a much faster rate more akin to what you would expect especially what you want when trying to clear a misted up front screen and then suddenly die back down again.At first i thought this must be an A2 trait but as i said after going over certain bumps in the road the interior fan speed is restored momentarily. Just the other night we went out and the car hit a bump in the road,nothing unusual there,our roads are shyte,and the fan kicked in at a much higher rate only this time stayed on for the rest of the journey which hasn't happened before.Whilst it was on full blast i could hear the fan speed hunting up and a down slightly as mentioned in the above post. It's obviously something electrical as this thread suggests. Has anyone else experienced this and how easy is it to reach this J126 fan controller?

Thanks

Mark.
 
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how very cool, i have been wondering why my fan does what it feels like - i just need to find out why the fan direction changes by itself, (as can be heard with the ingition on but engine not running)
 
to reach this J126 fan is not easy at all.
I took it out and I will try to repair it.
original part is 6Q1907521 in my 1.4 TDI
 
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