Using A/C fan as second thermofan
 

I dual Spals from the FM stage 2 fan kit, and I was thinking...can the A/C output be repurposed for a second thermofan. I have no A/C anyhow, so it was worth a shot. So I disabled AC control and set the DPO that is used for AC output as second thermofan. No joy.

Just curious if anyone else has thought about this and has a solution?

The condenser fan is on a different ECU pin than the AC clutch, except for on a 1.6 I think.

Are you running a PNP harness? And what year miata?

94 Miata and yes, I am runming the PNP harness. The guide says the AC output is on DPO2. So, my guess here is that without the compressor, this will not work?

No, just that on a 94 miata 1J is the AC clutch relay and 2S is the AC fan relay. You could jump the AC clutch wire over to the AC fan relay wire, or you could do it at the PNP harness. Not sure if they made that easy or not, but haltech support is quick to respond if you email them.

There's no reason it can't work without the compressor, just might need some custom wiring on your part.

Ah...OK. I can make that work. I can hear something click when I set the second fan to High. So there must be a relay for the AC clutch.

Yep, two relays. I thought the AC relay wouldn't work without the pressure switch being set, but I guess not in your case. I think it's inline with the relay control ground signal.

Then again Haltech might have jumped the AC relay with the condenser fan relay in the PNP board, then you would hear the fan relay click and not the AC relay. The fan works if you manually trigger it?

Actually, no it does not work using AC control. I removed the AC and jumped the plugs under the dash. This worked with the stock ECU, but not the Haltech.

This thread illustrates the issue:

https://forum.miata.net/vb/showthread.php?t=665097

The PNP must be setup for the 90-93 which appears to use a single relay for AC clutch and fan. Whereas there are separate relays in 94.

Just wanted to update this thread. Found an easy solution. As my previous post points out, 94+ have two relays for the AC...one for the compresser clutch and another for the fan. There are two output wires at the ECU. Haltech PNP is setup to work only with the clutch relay.

Rather than jumping the wires to activate the fan relay, there is an easier solution. At the AC sub harness, there is a DTM plug. Simply swap the pins at this plug and the Elite will now trgger the fan only. I set it up as a second thermofan that comes on at 205.

https://cimg0.ibsrv.net/gimg/www.mia...4f042b4648.jpg

These are the 2 pins to jumper inside the PNP box. pin 1, on the top right is the AC output. So tapped into that and into 2S. Have tested and can confirm that when the AC function is enabled that the AC clutch clicks and the fan also kicks on

Now, if only I could get the button on the HVAC controls to turn the AC on, as right now I am ready to buy a CAN keypad to make it work by forcing the function.

yes I have done something similar on the other side of the board last weekend, I used the 1l and 2s on the ECU connector side my wire was longer and I used a thinner wire gauge.

i have enabled the "Enable with A/C" option in the thermo fan 1.

So I've been thinking about this. I think I am gonna replace the wire with a diode. And also run a DPO either from the elite or the IO12 to the 2S pin. This way with the can keypad I can have control over engine fan, or AC fan. With the wire at the moment, if I do that with a DPO outputting to the same pin, it will feed back and turn both fans on.

I don't think a diode is necessary, you can enable with a/c in haltech setting it will do the same thing.

you can run a wire from 2s to DPO6 inside the circuit board, but of course you will have to double-check with a multimeter for continuity across the connectors and make sure DPO6 is actually not connected to anything in the OEM harness.

this way you will have two thermo fan setting in haltech to run the fans at different temps or switches + a/c switch, but if you wire 1l and 2s together yes this will run both fans at the same time but otherwise, you are more likely to forget to turn the fans on with a switch and overheat the engine the only reason you would need manual switch is to reduce the load on the alternator or turn on the fans with the engine off which there is a setting for in haltech.

if you need to turn the fans on with the ignition off, I think you need to use DPO6 to power the ignition switch and ignition source.

if you wire both fans together you will also have a spare DPO for other stuff like electronic waterpump or methanol kit etc.

I'm planning to repin the adapter or run wires across the circuit board for check engine light, brake switch, clutch switch, power steering switch, fuel pressure solenoid, evap canister.