I ran a jumper jumper from the original A/C fan relay (EA's weren't ECU controlled)
It's the yellow wire on the outer of the 2 A/C relays (The other is the relay for the Clutch power IIRC)
When the A/C is on, that relay will provide ground to that yellow wire......which is tied to the OE fan switch wire at the radiator.
Just tap it and run that wire over to your new fan relay and tie it to the same pin that the ECU trigger is on. A diode wouldn't hurt but not needed i don't think.
El Freddo, any chance you know which A/C???
Hmmm... I can't picture that in my head with the yellow wire and where it gets tied into etc I've got this setup in my L for river crossings and hot weather driving on sand or during hill climbs:
So in theory I take the ECU trigger and hook that into the back of my switch? What sort of diode would I need to protect the ECU, I would like to have that sort of protection!
As for the type of AC I've got, I think it's a Denso compressor - it certainly has never had the tab hanging out over the fan belts with that black box on it like every other L series I've come across. I'll have to check the compressor to be sure it's a Denso, shouldn't be hard to do as it's living on my bench at the moment!
With the AC cut relay hooked up, the compressor will turn on about a half second after pushing the AC button on the dash. I guess it's this way so the ECU can synchronize the IAC and the compressor solenoid, so rather than reacting to the compressor turning on it can do the two simultaneously so there isn't a hiccup in the idle.
Also I read that the ECU will cut off the AC when the engine is overheating; a nice feature too.
So if I've got this straight: Hook up the AC input wire to the ECU from the AC dash switch and wire in a normally closed relay so that the ECU can short the relay circuit and cut the power to the AC compressor/system? If so, that relay would look something like this (using the horn relay code):
Normally closed relay:
Power from AC switch = 30
"Other side" of the AC switch wiring to the compressor/AC system etc = 87
Ignition switched power (positive) = 85
ECU AC relay cut wire (Plug F47, pin 22) = 86
At the same time have the AC on input wired in from the switch before the above relay - this will have the AC switch tell the ECU the AC is on, even when the ECU AC cutout relay is in play. Have I got this correct?
Then the last piece to the puzzle is to wire in the thermo fan relay/trigger wire - hook into the yellow/black wire on the back of my switch ("auto mode") with a diode to protect the ECU so I can keep the radiator thermo switch in play. This setup should have the AC pressure switch already wired into the factory thermo wiring so no need to hook the ECU into this - but looking at the wiring diagram the EJ system has it the same, just that the ECU triggers it instead of a thermo switch in the radiator.
It's late over here, I've had a big day but I hope I've got my head around it - that's what I love about doing wiring conversions - get your head around it then it all falls into place and just becomes "easy" next time!
I also hope I haven't blown anyone's mind on this either! I've really enjoyed the reading with the last couple of posts thanks to Goyale and Presslab. I'm hoping you can confirm I've got his right, and if not, then correct my error or show a wiring diagram I can view. I believe I've got it all sorted correctly though.