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Old 06-13-2007, 08:13 PM   #1
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Default Finally FMIC but overheating now..

I really like 8psi. Perfect for an old man like me. Raced a 90's vette through the back roads and although he stayed with me, he still had to work at it. I love this car. Cody (www.lovefab.com) graciously gave up his Sunday and we installed an intercooler. (pictures as soon as I find the camera..) But we had to remove the stock radiator fan to be able to finish it in an afternoon. It actually still runs at the same temp but will overheat if I drive it hard for 15 minutes and then let it idle. I know, duh. I plan on installing a slim fan in the near future, but drag racing is friday night, so I need a quick fix. I wired the radiator fan wires to the AC fan wires and the AC fan does come on, but I have two questions:

Will the 12v from the AC switch mess with the variable voltage from the radiator switch and if not, can I use both fans for radiator duty once the slim one is installed?

Will the AC fan alone keep the car from overheating? (I'm not going to be able to test it until Friday evening)
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Old 06-13-2007, 08:54 PM   #2
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most likely not enough... you should be able to source 12v from the main fan at least, keep the same ground.

dump all the fluids and do a 70/30 (70=water).
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Old 06-13-2007, 08:59 PM   #3
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I don't understand most of what you are asking. What is a variable voltage switch?

Did you run the +12V from the driver's side fan to the +12V from the passenger side fan? The A/C fan +12V goes to ground when the A/C is off, so you'll blow your main cooling fuse, and possibly the relay as well.

Yes, just the A/C side fan should be sufficient for what you need. I depowered my main cooling fan for 2 days to test out my A/C fan mod.
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Old 06-13-2007, 09:11 PM   #4
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I was assuming the voltage varied for the radiator fan because it has different speeds versus the ac fan which only runs full on. That *** in assume again thing.
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Old 06-13-2007, 09:12 PM   #5
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Quote:
Originally Posted by Ben View Post
Did you run the +12V from the driver's side fan to the +12V from the passenger side fan? The A/C fan +12V goes to ground when the A/C is off, so you'll blow your main cooling fuse, and possibly the relay as well.
Thats the kind of info that saves my ***.
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Old 06-13-2007, 10:58 PM   #6
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If the AC switch turns on both fans anyways, why not just have both fans hooked to the cooling fan connector all the time and not even use the AC connector?
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Old 06-13-2007, 11:00 PM   #7
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Quote:
Originally Posted by rotaryjunky View Post
Thats the kind of info that saves my ***.

yeah, forgot to mention to cut your existing 12v line to the the a/c fan; basically just follow the parrell fans writeup so you'll at least have a working fan like normal.
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Old 06-13-2007, 11:06 PM   #8
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Quote:
Originally Posted by rotaryjunky View Post
If the AC switch turns on both fans anyways, why not just have both fans hooked to the cooling fan connector all the time and not even use the AC connector?
You can do that. But I'd do it with a relay.

I gave someone on m.net instructions on how to do it with a relay... Let me see if I can find it...
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Old 06-13-2007, 11:08 PM   #9
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http://forum.miata.net/vb/showpost.p...0&postcount=12
Do it this way. A good relay is BWD R3177 from O'Reily's. SPDT $8.

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Old 06-13-2007, 11:35 PM   #10
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Thanks, I saved the link. So this way, the AC only turns on the ac fan and the cooling relay turns on both instead of stock where the cooling relay just turns on the cooling fan and the AC turns on both fans. Whew. Right?
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Old 06-14-2007, 12:14 AM   #11
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yeah, pretty much, but the cooling fan relay is tripping another relay to spin the a/c side fan so it doesn't add any additional load to the cooling fan circuit. that's the best way to do it. though dudes have been getting away doing it the ghetto way, I wouldn't.
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Old 06-14-2007, 10:24 AM   #12
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Hey Ben....

So I've currently wired an AC side fan to turn on with the cooling one, via the relay method. However, I don't presently have AC.... When I install the AC I got... are there any mods required to the current wiring? Or just plug in and go...?

It's presently.... cooling fan t'd to relay "source". 12v hot to relay from the fuse box, + ground. To the hot wire into the AC fan (I tapped to leave the connector on there....) then I have a ground wire for the fan. If the AC circuit will put the fan to ground, when not in use, am I going to blow fuse?

Will check your m.net thread.... but I haven't started reading over there yet.....

Dave,
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Old 06-14-2007, 10:58 AM   #13
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The BEGI scooper, it saved my over heating problems.
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Old 06-14-2007, 11:16 AM   #14
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Yeah if you're using stock wiring, the a/c relay shunts to ground when the a/c is off. When that happens, if you've just "tapped" power from the cooling fan to the a/c fan, you will loose your cooling fan fuse (fusible link--$3).

I didn't realize that the a/c circuit went to ground when I first wired up my dual fan mod with a SPST relay. So I blew the fusible link and for some reason, the cooling fan relay. With an added SPDT relay, the A/C circuit is isolated from the cooling fan circuit, but either circuit can activate the fan. Also there is no extra strain put on the cooling fan circuit as the a/c fan will draw power on its own.

If it were my car, I'd also put a little delay circuit in there too to make one fan turn on a second or two after the other. It would be easy, a transistor, cap, and a diode should do it.
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Old 06-14-2007, 01:10 PM   #15
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Thanks... I'm glad this came up, otherwise I would have been loosing a few fuses.....

Dave,
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Old 06-17-2007, 07:15 PM   #16
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With a 3" thick IC Im getting overheating issues now. I think Im gonna go with a more thin IC on my next miata project w/ an aluminum radiator and some SPAL fans.
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Old 06-19-2007, 02:25 PM   #17
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did you do an over the radiator IC pipe install? I was pondering my pipe routing this weekend and noticed that the AC fan is more slim than the other one. I was thinking about switching the cooling fan for another AC fan in order to make more room for moving the radiator.
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Old 06-19-2007, 02:33 PM   #18
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My cooling fan pushes a lot more air than the a/c fan when I feel behind them with my hand. Don't think I'd want 2 a/c fans...
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Old 06-19-2007, 03:00 PM   #19
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its like 1200CFM vs. 1600CFM or something.
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