R32 - Have Your Overheat Fan Turn On With Your A/c

[Ben C34]

This is some seriously in depth electrical discussion going on.

How do magnets work anyway?

[Ben C34]

Actually this is next level funny that it has been over two years and you can't get it to work!

I now completely understand your rage. I would be mega angry if I was that bad at comprehension.

[r32-25t]

Sounds like the car is not jdm yo YouTube spec enough and needs to be sent to the wrecker 

[Phyco]

At risk of raising this thread from the dead, I've just tested this mod on my R34 and would like to see if anyone can assist with some minor troubleshooting.

I've bridged the trigger pins between the AC and Auxiliary Fan relays, which works to trigger the Aux Fan to start with the AC Compressor (perfect) but the problem now is that the Auxiliary Fan is staying on after the ignition is turned off, unless I remove the bridge on the trigger pin. I can't seem to figure out why it's happening to determine a path forward, other than just concluding that nothing is triggering the Aux Fan relay to 'off' state, and that it has constant power due to the overheat function allowing it to continue running when the ignition is turned off.

For reference here is the pin-out on the R34 (GT-T Series 1).

Auxiliary Electric Fan Relay
Pin #3 [black wire/white stripe] connects to 30A Fuse (F/L - 7)
Pin #5 [black wire/yellow stripe] connects to auxiliary fan motor positive
Pin #2 [green wire/yellow stripe] connects to 10A fuse (#13)
Pin #1 [green wire/brown stripe] connects to ECU port 78 (Auxiliary electric fan relay control signal) <--Trigger

Air conditioner Relay
Pin #3 [purple wire] connects to 10A fuse (#35)
Pin #5 [blue wire/yellow stripe] connects to air conditioner compressor positive
Pin #2 [purple wire] connects in-line to pin #3
Pin #1 [green wire/red stripe] connects to ECU port 14 (Air conditioner relay control signal) <--Trigger

 

 

Thanks in advance for any suggestions.

[GTSBoy]

If there was no other funny business going on, and looking only at the wiring diagram, I would say:

     The logical conclusion has to be that when the engine is switched off, the AC control pin 14 on the ECU is switched to earth. I'm not sure why they would do that, but that is the only way for the fan relay to remain powered.

Because you bridge pins 14 and 78 together, you have no way of being able to test which of those is actually being held low by the ECU while they are connected.

What I would do to try to gain information is test for continuity to earth at each of those, when they are not bridged, and in each of the cases where the respective circuit is active and not active. Probably safest to use a voltmeter rather than continuity tester, because there is 12V on those pins when they are not active. So that is check for 0V at pin 78 when the A/C is on (ie, should be switched to earth by the ECU), off (should be not be switched to earth, should read 12V). And do the same for pin 14 when you have triggered the aux fan by shorting the temperature switch (for the ON case) and when it is not running.

Then repeat all that with the bridge in place, just to make sure that the earth is being created in the ECU (which is the only thing I can imagine). None of this solves your problem, but you know now the behaviour in detail.

Next thought:

     Perhaps the aux fan is held on for some time (ie, by an ECU timer) after the ignition is turned off, if the fan is active at the time the ECU is switched off. You can test this by testing the behaviour of the aux fan on its own. I would be:

• Triggering the ECU input at the temp sensor by shorting (with the engine running), remove the short and see if the fan stays on for a while even after the input goes away. If so, there is most definitely some type of delay that always happens.
• Do the above but turn the engine off while the fan is still running on delay (assuming it does, from above) and see if it stays running with the ECU switched off.
• Do the above but leave the temp switch shorted while you turn the ECU off. This probably proves not much, if you have already learned from the above points anyway.

 

Then, we get to shenanigans. Maybe it is wrong and silly to bridge 14 to 78 because the ECU can't handle it. Maybe it creates a circuit latch inside the ECU that you can't break. In which case, you can't do it this way. If that's the case, then I would suggest attacking the problem at the root. You want the AC to activate the aux fan? Then get the AC actuation signal to switch another relay that shorts the aux fan temp switch. The relay will just bypass it. When the AC comes on, the ECU will also get the hot signal and run the fan. When the AC is switched off, the relay will drop out, the bypass around the temp switch will drop out and the wiring should look exactly like it did unmodified.

[Phyco]

11 hours ago, GTSBoy said:

If there was no other funny business going on, and looking only at the wiring diagram, I would say:

 ...

Thanks for the detailed response. The point about the ECU switching the control pin to earth when the ignition is turned off makes sense.

As for shorting the temperature switch, that may be more difficult. The R34 doesn't have the same setup as the R32 does with a temp switch in the radiator to control when the aux fan is triggered (there are no sensors in the radiator at all). I don't know exactly what logic the ECU uses to determine when to trigger the aux fan, but from what I have been able to determine online it's a combination of values from the coolant temperature sensor in the water inlet on the intake manifold, and the AC pressure switch (ECU pins 56 & 57, respectfully). I could short the temperature sensor here but I have no idea what else uses it, nor do I know whether it alone will actually trigger the aux fan anyway.

I'm leaning towards 'working around' the problem if there isn't a simple solution I'm missing here. I know the aux fan draws 12v/80w max so roughly 6.7A, and more than likely when the weather is hot I am always going to have the aircon running, so I could unpin the fan wire from the aux fan relay entirely and connect it to a suitable new relay with a power source that is only hot while the engine is running, and use the AC relay to trigger it.

Here is the full ECU pin-out if that is any help to anyone (either with this, or in future).

[GTSBoy]

Your 2nd relay idea is valid, but you can just put the switched side of it in parallel with the original aux fan relay, so they can both turn it on.

[Phyco]

Well we got there. Turns out the diode mentioned in the original post as a method to prevent the overheat function turning on the aircon on the R32, actually works to make this functional on the R34. I bought a pack of 1N4004 from Jaycar ($0.95) and added one inline, with the cathode towards the AC relay. Everything behaves as expected now!

Thanks for your help @GTSBoy

[GTSBoy]

Ah. If you'd said that the original R32 instructions called for a diode, I would have said "well, duh!". If you did it without a diode then you were putting yourself directly into the "other funny business" category that I started with.

Glad you got there with minimal trouble in the end.

[Phyco]

Yeah, initially the reason I didn't think to include it was that it was noted as optional on the original post to prevent the overheat function triggering the AC, and not as a requirement for the mod to work. That may be due to things being setup a little differently in the R34. Oh well, at least this is here for anyone who may come across it in future.