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Old 01-19-2009, 09:25 PM   #1
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Default Parallel Fan jumper at ECU wiring?

I was told this is possible, and 30 minutes of searching confirmed that it's possible by dropping one of the wires to ground, and Joe's AC FAQ gave me a hint, but I'm still not sure.

I have two 11" Spal low-pros on a custom ABS shroud (all of that magically appeared the last couple of days). I have the main fan kicking on normally, and I want to wire the AC fan to kick on with the main fan when a switch is on, or not at all when the switch is off.

CLTs low, switch on: neither fan on
CLTs high, switch on: both fans on
CLTs high, switch off: main fan on, AC fan off

I searched for like half an hour. My idea is to jumper the AC trigger wire to the main fan trigger wire at the ECU and add a switch inline. What pins am I jumpering?
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Old 01-19-2009, 09:43 PM   #2
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check out this thread. As long as you no longer have A/C you're golden.
http://forum.miata.net/vb/showthread...&highlight=fan
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Old 01-19-2009, 09:47 PM   #3
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to tie main fan and AC fan on '94, that'd be 1L and 2S, then put a SPST switch on the 2S line. when the switch is closed, the A/C fan (marked "condenser fan" on the 94 wiring diagrams) will never turn on. when the switch is closed, it will be on whenever 1L/2S is grounded.

this is all based off the Yorba Linda wiring diagrams for 94, pp 1, 5, and 8.
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Old 01-19-2009, 11:46 PM   #4
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A wise man started this thread a while back. It's based off the 1.6L but it still may help...
https://www.miataturbo.net/forum/t19315/
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Old 01-19-2009, 11:51 PM   #5
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Badass. Thanks. J Man's post on M.net confirmed 1L (color Black/Green) and 2S (color Blue/White).

edit: Schematics are in this thread: https://www.miataturbo.net/forum/t13676/

Last edited by Savington; 01-21-2009 at 03:15 AM.
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Old 01-19-2009, 11:57 PM   #6
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it would be pretty easy.

Connect a $1 toggle switch between 1L (blk/grn) and 2S (blu/wht) on your harness.


1L is the main fan relay ground. 2S is the condenser fan relay ground.


With the switch off your main fan will work however you have MS controlling it. (low coolant no fans, coolant high main fan)

With the switch on, the a/c will turn on with it. (both fans on)


edit: looks like i was too slow.
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Old 01-20-2009, 12:01 AM   #7
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Will MS be triggering the main fan? If so, what output will you be using? The stock transistors are only rated at like 200ma IIRC, which you will exceed running two fans relays. You can change them out for bigger ones though. Or do what I did and just use the FIdle circuit to drive them as it's rated for 1.2A. Plenty.

I've got extra outputs on mine so one day I want to separate it so that one fan comes on at say 220 and another at 230.
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Old 01-20-2009, 12:03 AM   #8
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I've had mine jumped for months now with no ill effect... Just wanted to throw that out there.
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Old 01-20-2009, 12:06 AM   #9
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if you wanted to get fancy with a fail safe, you could wire a second switch or maybe dpdt switch that will force to ground regardless of the MS.
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Old 01-20-2009, 12:10 AM   #10
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Quote:
Originally Posted by patsmx5 View Post
Will MS be triggering the main fan? If so, what output will you be using? The stock transistors are only rated at like 200ma IIRC, which you will exceed running two fans relays. You can change them out for bigger ones though. Or do what I did and just use the FIdle circuit to drive them as it's rated for 1.2A. Plenty.

I've got extra outputs on mine so one day I want to separate it so that one fan comes on at say 220 and another at 230.
I'm almost positive the MSPNP uses something else, not the 2N3904 which is not sufficient for one fan.; more than likely a 2n2222. I use a ZTX450-ND in my builds; 1000mA.
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Old 01-20-2009, 12:16 AM   #11
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WOOT! Thanks brain for the 1000mA of coverage! lol Sav looks like ur covered too with that 600mA transistor.
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Old 01-20-2009, 12:25 AM   #12
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Quote:
Originally Posted by MikeRiv87 View Post
WOOT! Thanks brain for the 1000mA of coverage! lol Sav looks like ur covered too with that 600mA transistor.

yours I more than likely built with a 2n2222 at 600mA.
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Old 01-20-2009, 12:50 AM   #13
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Quote:
Originally Posted by Braineack View Post
I'm almost positive the MSPNP uses something else, not the 2N3904 which is not sufficient for one fan.; more than likely a 2n2222. I use a ZTX450-ND in my builds; 1000mA.
Ah. Yeah, I got the 2N2222's in mine now. After killing a 200ma one. Not even using them as I switched it to FIdle after it died, then replaced them.

if he wanted to get fancy, he could put a diode between the fan control wires with the banded end on the main fan side, then run a wire from the A/C fan side to a SPST swtich that goes to ground.

Then he gets main fan works like normal when MS says to. And if he flips the switch, both fans are on regardless of what MS says. Hot side of relays is still controlled by key so you can't accidentally leave them on.

Then do the fans like sav originally said. You'd have 2 swtiches, but by god you could make the fans do whatever you wanted.
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Old 01-20-2009, 08:49 PM   #14
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diy told me to jump the GND's from the fan output to the ac output at the computer. My fans still don't work, so I haven't done this yet.
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Old 01-20-2009, 10:18 PM   #15
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I just added a relay to trigger the A/C fan when the engine fan kicks on. Took me less time then to read this thread and to respond.

Engine hot = both fans
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Old 01-20-2009, 10:20 PM   #16
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Anyone want to tell me how I could wire this so the A/C wouldn't come on when its fan came on?
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Old 01-20-2009, 10:41 PM   #17
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Quote:
Originally Posted by Eraser-X View Post
I just added a relay to trigger the A/C fan when the engine fan kicks on. Took me less time then to read this thread and to respond.

Engine hot = both fans
You added a relay, ground, hot wire, and trigger wire, then mounted the relay, ran the trigger wire to the trigger wire for the main fan, and ran the hookups from the relay to the AC fan.

I jumpered two wires at the ECU harness.

My is way easier.

Last edited by Savington; 01-21-2009 at 03:18 AM.
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Old 01-20-2009, 10:56 PM   #18
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Quote:
Originally Posted by Eraser-X View Post
I just added a relay to trigger the A/C fan when the engine fan kicks on. Took me less time then to read this thread and to respond.

Engine hot = both fans
wanna help me trouble-shoot my fans this weekend? I has a multi-meter.
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