Repair of electronic interior fan controller

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My Name: Ozvtr

Posts: 1043
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
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The fan speed controller for the MK1, MK2 and facelift C3's climate control is electronic. Consequently they tend to break from time to time.
The usual suspect in this case is the failure of the main driver transistor. This regulates power to the interior fan. I think the main reason it fails is because the heatsink paste dries out. The heatsink paste conducts heat away from the transistor and into the big aluminium heat sink.
If you have a bit of electronics knowledge and can wield a soldering iron, then you can repair the speed controller quite easily.
Don't worry if you don't think you can repair the speed controller, replacements for the whole speed controller unit are available for less than 10 pound.
Incidentally, the genuine thing and the cheap Chinese knock-offs are IDENTICAL IN EVERY WAY!!!! The only difference that I found was the small part number label and the green Q.C. paint on the transistor retaining bracket. I believe they all are made in China and the "genuine" ones are "assembled" in France. So don't be afraid to buy a cheap Chinese one, its exactly the same as a genuine one.
Update: I had cause to buy another one from Ebay and it was NOT identical to the others. It's construction was slightly inferior to the other two but it does still perform the same.

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This is a video on how to remove the speed controller. Forget about the bit with the glove box, the car is left hand drive. Go straight to the 1:30 minute mark.

This video goes through a full inspection of the connector solder joints as well as replacement of the MOSFET. The connector contacts and solder joints can also be a point of failure.

Remove the front and back covers by inserting a thin bladed screwdriver under the tabs.
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The electronics and the driver transistor can now be seen.
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Check the four BIG contacts in the green connectors. Check the plastic around the metal contacts. If any of them are discoloured, the plastic is melted or the solder is grainy and sunken, I would replace the whole speed controller. The guy in the video goes through the rigmarole of removing and cleaning the contacts. I wouldn't bother. For the cost of a whole new unit it's not worth it. The contacts in mine were fine.
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fan0 003.jpg
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Remove the transistor retaining bracket and then lever the transistor off the heat sink. The transistor will be stuck to the heatsink, some force might be necessary. De-solder the two outer legs of the transistor from the printed circuit board. The center leg is connected to the transistors back plane. So be prepared to use a bit more heat to de-solder the center leg.
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install the new transistor onto the heatsink using new heatsink paste. Trim the three leads to size. Solder the two outer leads in position. lever the transistor up a bit away from the heat sink. Solder the center lead. Bend the transistor down and install the transistor retaining clip. Snap the front and back covers into position.

The transistor is a Fairchild HUF75344G. An N-channel >60V >60A MOSFET in a TO-247 package should do the job but the 75344's are easy enough to find. I found them on Ebay from china for a pound or so.

speedcontrol 005.jpg
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I wouldn't bother testing the MOSFET as it is very cheap and easier to just replace it.
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