A little help understanding this wiring scheme

[WidowmakerS2]

I'm at it again with trying to wire up the 500W fan in my coupe. The way it is now, I've got full speed only, and run a risk of the fan motor spinning the fan blade off the axle on startup.

However Saltinot explained this to me last year, and I've got all the relays, wires and fuses needed.
My experience with 12V wiring is limited to some bodge jobs, my 7a-3b conversion and wiring some headlights.

I've moved the battery to the trunk to make room up front. I have got a +12V point where the battery used to be though.

The way I see it: (please correct me if I'm wrong)

-I can use the signals (including power from S15) from the sensor on the rad, as they have no other function than to control the rad fan.

-I have no use of the E1 terminal on the resistor pack, as I have no after-run curcuit.


What I'm wondering

-30 on the scheme is +12V continous while X-is switched. Where do I get +12V to run the Medium and high speeds without frying something else?

[Error404]

This should help
http://www.s2forum.com/forum/showthr...ght=ABY+fan+7A

[WidowmakerS2]

I think it does

[johne]

The way I see it: (please correct me if I'm wrong)[/B]

-I can use the signals (including power from S15) from the sensor on the rad, as they have no other function than to control the rad fan.

Yes

-I have no use of the E1 terminal on the resistor pack, as I have no after-run curcuit.

Correct


What I'm wondering

-30 on the scheme is +12V continous while X-is switched. Where do I get +12V to run the Medium and high speeds without frying something else?

From the big terminal on the back of the alternator via a 60 amp in-line fuse.

Your diagram isn't quite right as the medium speed relay isn't doing anything and is always on. You only need two relays as the temperature switch in the radiator only has two sensors.

Refering to your diagram, the high speed relay wiring is correct. Remove the medium speed relay. Rename the low speed relay the medium speed relay and connect it to E2 on the resistor pack. As you say yourself you have no need for the E1 terminal as you have no after-run circuit.

In your circuit you could just join the X line and the 30 line. If you did that the fan could come on at any time and would stay on after you've switched the engine off if the radiator was still hot. Good for cooling the engine but a possible safety hazard and trigger for any security alarm you may have which is why Audi didn't do it that way until forced to add an after-run circuit.

John

[WidowmakerS2]

Thanks John!

I started on this job today. I did mostly what you wrote, but I got the 12v from the 12V point I've got in place of the battery tray. Makes for some longer cables, but other than that it's pretty much the same.
I hadn't thought about the 30/X issue. One possibility is to add a switch to S15, or even rewire that to 12v-switched.

[WidowmakerS2]

I did as I wrote above. The car tood idling for some time, but the fan did not start. I'm not sure when the fan starts normally.

It does however start when I press ECON or off on the AC control.

[johne]

That all sounds correct. Fan won't cut in until temperature gauge has reached just over 90 in my car.

John