All the years I've had my 944, the cabin fan has been very feeble. I don't think position 1 does anything, 2 is barely noticeable, and 3 is faster, but not enough to clear a really misty screen. As I understand it, this is because the resistors have become too resisitive! Annoyingly, early 944's and all 924's have the resistors hard-wired to the loom from the switch, and I think the loom is NLA.
I had two possible solutions:
1) Buy some resistors of the correct values, and solder these in place of the originals.
2) Buy a DC fan controller on recommendation of someone else on this forum.
I choose option 2, as it included a variable speed knob, and seemed a more sophisticated solution. But this proved to be hard to wire in, as I couldn't track down the positive feed to the fan. The switch and resistors are actually wired AFTER the fan, so technically on the earth side. Also the fan controller would need a direct positive AND negative to the motor, so I filed that device in the "too hard" box.
Whilst testing and probing the switch, I stumbled across a solution. One of the wires that leads to the resistors is not even connected to the switch! This appears to be a direct wire to the circuit AFTER the motor, but BEFORE any of the resistors, so bridge these, and the fan gets the full 12v (or 14v-ish if engine running). I realised I could remove all the spade connectors from the switch, and put them back in different places. The gist is this:
- Switch position 3 leads to no resistors
- Switch position 2 leads to resistor 3
- Switch position 1 leads to resistor 2
- Unused spade terminal leads to resistor 1
The final wiring can be seen here:
Attachment:
Alt fan wiring (Small).JPG [ 86.59 KiB | Viewed 5036 times ]
Hope this helps other people.