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Old 08-24-2012, 10:57 PM   #1
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Default Cooling fan not coming on

Driving home today I noticed my car getting a little warm when stopped. Came home, checked the fan and it wasn't coming on.

I hit the AC and that fan came on. I swapped the relays and the AC fan still worked, so both relays are good. I connected the fan directly to a battery and the fan comes on. I checked megasquirt and it's reading the correct water temps. I did swap the radiator a few weeks ago, but it's worked fine since then.

Any idea what's broke or how to fix it?
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Old 08-25-2012, 08:51 AM   #2
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Short in the signal wire to the relay?
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Old 08-25-2012, 09:22 AM   #3
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The "maybe a random wire fell in half somewhere" theory was about all I've been able to come up with too

Thanks for the input. I was hoping there was something obvious I missed. Forgot to mention in the first post, fan fuse in the engine bay looks fine too.
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Old 08-25-2012, 12:05 PM   #4
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Are both fans on when you press the A/C button?
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Old 08-25-2012, 02:04 PM   #5
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No, just the passenger side fan.
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Old 08-25-2012, 02:07 PM   #6
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1) If you ground the fan relay pin, does the relay and fan activate?
2) How are the fan circuits inside the MS built?
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Old 08-27-2012, 04:01 PM   #7
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Subscribing to this thread.
I have a off-the-shelf MS3 that will turn the fan on, but it seems to be on a switched circuit. I'm wondering if I'd be better off to mod the MS or just simply run constant power to my fan relay.
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Old 08-27-2012, 04:03 PM   #8
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Quote:
Originally Posted by pdexta View Post
No, just the passenger side fan.

well it's possible the main fan is dead. ground TFA and GND in the diagnostics box to confirm the relay/fan is still working

Quote:
I have a off-the-shelf MS3 that will turn the fan on, but it seems to be on a switched circuit. I'm wondering if I'd be better off to mod the MS or just simply run constant power to my fan relay.
who built it? did i? what circuit is the fan output going to through? do your software settings reflect this?

this isn't hard.
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Old 08-27-2012, 04:08 PM   #9
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Quote:
Originally Posted by Braineack View Post
well it's possible the main fan is dead. ground TFA and GND in the diagnostics box to confirm the relay/fan is still working
Per the first post, he swapped relays with the A/C fan, and the A/C fan still worked. He also applied battery power to the fan and it worked. So both the fans and the relay are ok - something is wrong either with the wiring (easy to diagnose in this case where the fan does not work, period) or with the MS fan relay circuit.
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Old 08-27-2012, 04:11 PM   #10
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or a parameter not turning on the correct output...
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Old 09-14-2012, 12:14 PM   #11
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happened on my uncles Miata.

he ended up wiring everything with a manual switch (was tired of trying to chase down the real problem).
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Old 09-14-2012, 12:22 PM   #12
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I had a problem with my fans (wired together, no AC) and it turned out to be the connection at the thermostat.
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