thermo fan operation / driving too cool

[Pandave]

hey all. went for a spin yesterday with the kids in creswick state forest. was a bit cold and humid so needed the windscreen demister on. i have dual thermo setup than both turn on with a/c and when temp rises. problem was that with the demister on in cold weather both fans activate, making the car run too cool. if i read the fsm correct there are two wires to activate the factory fan. one for a/c and another for engine temp. what i need to know is which and where is the engine temp wire so i can wire it up to the main 16" thermo fan only, so when the a/c is on just the factory fan activates.

[rainman]

My understanding was that the pcm switches on the aux fan by grounding the relay in the fuse/ relay box. Which inturn supplys power to the fan.
The pcm uses imputs from the ac circuts, and from coolent temprature to decide when to turn the fan on.
I.e. The pcm turnes the aux fan on the same way in both instances, it grounds the control relay.
The thermostat is what is supposed to regulate the min operating temp of the engine, it is present/ working/ correct temp rating?
I have twin electric fans as well, if you realy wanted to run the primary fan on engine temp only, maybe get a watchdog unit- digital temp gauge with relay control, or if you look at your thermostat housing you will see a casting boss that could be drilled out to accept a 100*c temp switch, and use that to operate the primery fan. I have thought about such things, but tbh the system i have now works very well.if it aint broke........

[junglejuice]

I don't think you will find this a suitable option as the "wire" for the engine temp control is also what tells the ecu what temp the engine is for the mixture settings, the ecu then tells the fan to turn on, I don't know that the aircon uses a different control for the aux fan, it may also send a signal to the ecu.....