Wiring-in switches into factory a/c fan harness

[spooled240]

What's up zilvia. I currently have altima efans that I've wired in using the stock a/c fan harness on my '97 s14. I wired in two more relays in the stock fuse box for the second fan with direct power to the battery - it's legit. They work great, unfortunately the ecu turn the fans on at about 95 degrees celsius, which is about 203 degrees Farenheit - either way, it's too hot.

I want them to come on at about 185 degrees Farenheit with a manual override switch.. BUT I also want the stock functionality of the fans turning on automatically whenever the a/c is activated. It will also act as a safeguard the thermoswitch ever fails. I've been looking at wiring diagrams and I think this may be possible with this setup:
https://farm8.staticflickr.com/7415/16457852471_3ab37fa4f0_b.jpg

I know this is only feasible if the ignition switch supplies the voltage to the circuit and the ecu provides the ground. My only question (and it may be a stupid question) is if the ECU grounds the circuit or if it sends the circuit power?

I'm not sure what to make of this: :confused: It looks as if the ecu is constantly powering these wires with voltage?
https://farm8.staticflickr.com/7344/16273880887_d738e0da2b_b.jpg

[dbeiler]

The wiring diagram posted shows the high and low fan relay electromagnets being powered by the Ignition Switch. Power is coming from the ignition switch via the L/OR wires to terminal 2 on each relay. Therefore, to operate the relays, the opposite end of the electromagnet (terminal 1) is being grounded by the ECM.

Those data values posted in the second pic, would be the tested voltages with the ECM disconnected. You'll save yourself a lot of confusion by using the regular cooling system wiring diagram instead of the Trouble Diagnosis diagram you have posted.

To answer your question, yes, the ECM grounds the circuit.

[jedi03]

I would say if you want it on sooner get aftermarket control...but 203 isn't to hot...operating range is usually 190 to 210...I have my fans set to come on at 220 which is factory for the altima and I never seem to see with driving my sr around...

[spooled240]

The wiring diagram posted shows the high and low fan relay electromagnets being powered by the Ignition Switch. Power is coming from the ignition switch via the L/OR wires to terminal 2 on each relay. Therefore, to operate the relays, the opposite end of the electromagnet (terminal 1) is being grounded by the ECM.

Those data values posted in the second pic, would be the tested voltages with the ECM disconnected. You'll save yourself a lot of confusion by using the regular cooling system wiring diagram instead of the Trouble Diagnosis diagram you have posted.

To answer your question, yes, the ECM grounds the circuit.

Thanks, I'll look into that. I checked the voltage of the relay coil wires with the ignition switch on and I saw 12 volts, so that would make sense. If this is the case then wiring in the thermoswitch and the manual switch would provide alternative grounds to turn the fans on sooner/at will?

I would say if you want it on sooner get aftermarket control...but 203 isn't to hot...operating range is usually 190 to 210...I have my fans set to come on at 220 which is factory for the altima and I never seem to see with driving my sr around...

Yeah i know its not crazy hot, but not ideal especially for the turbo setup I'm currently running in socal :P

[jr_ss]

You could use a seperate thermo switch to power the larger fan on and then use the smaller fan as a factory setup. One fan on at 185, two fans on at 203. This would probably be the easiest route and you could still use the aux switch as intended.

[spooled240]

I thought about that. Only problem with that is only one fan would be on when the a/c is switched on. The a/c works decent with one fan, but it works so much better with both fans on. It's probably the coldest a/c I've ever felt lol

Did a bit more digging in the FSM and found this. I can't believe I missed it earlier. Terminal 2 is supplied with voltage with the ignition switch on.
https://farm8.staticflickr.com/7282/16485178185_322d6f4640_b.jpg

So I think this just about confirms that the ecu grounds the circuit. I will manually ground the circuit to see if the fans turn on.

[jr_ss]

Generally speaking the ECU always grounds a circuit.

[gawdzilla]

your proposed wiring diagram will work, but you will lose the high/low functionality of the fan obviously. i don't have AC or a manual override switch, plus my thermoswitch controls an oil cooler fan, but conceptually it is the same diagram you have. and yes, the ECU controls the ground.

why don't you just add a manual switch and forget the thermoswitch? that way you can retain high/low from the ECU when your manual switch is OFF.

Or are you planning to cut pins 13 and 14 to the ECU?

[spooled240]

I should still have the functionality of the high/low fan control since I'm going to keep the ecu connected to the circuit. I am merely adding additional grounds that would kick the fans on whenever the thermoswitch or manual switch is on. I still want the ecu to turn the fans on at 203F or whenever the a/c fan is on.

[gawdzilla]

that'll work then. go for it.