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Old 03-24-2004, 08:15 PM
horvath's Avatar
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Wiring an electric fan w/relay

Does anyone have a schematic for wiring an electric fan with a relay and temperature sensor?

I just had this one installed:
Walker Radiator w/16" Electric Fan

I'm curious about the way my mechanic wired this puppy ... I want to take a closer look at it this weekend and see if I agree with what he did. I think he has a wire going directly to the battery and that's bugging me; it doesn't make sense to me -- shouldn't I run a wire from my fuse box to power it?

Thanks for any help.

Alan
54 Chevy Pickup

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Old 03-24-2004, 08:36 PM
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Yes, it should be fused, and run from a relay.

Vince
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Old 03-24-2004, 08:59 PM
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Thanks, Vince

What's the order? I'm guessing I should take a wire from my fuse box (I have a few that aren't assigned to anything) and run it to the relay ... the relay goes to the fan ... yes?

Does it need to be a heavy wire? I'm guessing it doesn't because of the relay.

How do I determine which fuse-size to use?

Alan
54 Chevy Pickup
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Old 03-24-2004, 10:07 PM
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You could run an inline fuse. about 20 amp?
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Old 03-24-2004, 10:30 PM
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That looks like a painless relay kit, I used the same one to put dual fans on my truck, there should be a main red power wire running from the battery to the circuit breaker then to the relay and then there should be a smaller 16 gauge I believe gray wire that runs into the fuse panel to either a keyed or constant 12v supply. Yours must be hooked to a keyed source right now if they shut down when the key is off. I ran mine through a rocker switch so I can shut them down when I want. I will look to see if I still have th schematic that came with mine and will try to post it.
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Old 03-25-2004, 06:42 AM
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Found this on the Vintage Air web site, it is what you need.

http://www.vintageair.com/downloads.asp

Vince
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Old 03-25-2004, 08:23 AM
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this is a wiring diagram for a fuel pump, BUT they all wire up the same, just wire it as though your using your fan instead of the fuel pump....joe



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Old 03-25-2004, 08:57 AM
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Only thing I would ad is that I run a 10ga wire from the fuse block to the relay to the fan, just because. 14ga sounds a little anemic to me.
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Old 03-25-2004, 10:00 AM
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Thanks, Muncie -- I don't understand why there would be a main wire from the battery to a circuit breaker when there's a wire from the fuse box as well. Isn't that like a double power source??

Thanks, Vince -- The Vintage Air wiring diagram is a real help.

Thanks, TooMany2count.

Thanks, Willys36 -- maybe THAT'S my problem!?

It's kinda wet outside today, but I'm gonna try looking into this. My Voltage gauge has been acting funny since we installed this fan and swapped the gear drive out for a double roller timing chain. When I'm sitting at a red light my rpm's will sometimes take a sudden drop and it seems the voltage starts reading below 14. I tried raising the idle, but it still does the same thing regardless, so I'm thinking something may be drawing more power than it should and I suspect the fan because it's been recently added into the picture.

PS -----
Check this out:

I just called my mechanic and talked to him about this. He says it's the fan ... because I have a temp. sensor in the picture, the DRAW created when the fan turns on is what's causing the surge that's slowing the engine down.

So, he says if I disconect the wire that goes to the temp. sensor and gound it, the fan will run all the time; the surge won't happen, and I'll be okay.

THAT sounds like the easiest fix ... only will my engine run too cold? Will I need a different thermostat (I have a 180* in now)? He says, "no."

Alan
54 Chevy Pickup

Last edited by horvath; 03-25-2004 at 10:00 AM.
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Old 03-25-2004, 11:37 AM
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I have the thermostatic switch on my car and don't notice any problem when it kicks on. Unless it actually kills your engine, leave it hooked up. Saves wear and tear on your fan, increases fuel efficiency since alternator isn't generating extra wasted power, engine runs @ proper temperature - all around a good idea.
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Old 03-25-2004, 11:52 AM
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Thanks, bro'

It's never a problem when I'm driving ... only when I'm stopped and in gear ... I think the engine would stall if I didn't slip it out of gear or hold the brake with one foot and give a little more gas with the other.

What do you think I should do? A fatter wire to the battery? A bigger & better alternator?

Alan
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Old 03-25-2004, 12:15 PM
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Horvath check out this site www.painlesswiring.com it will show you how you relay is wired up. The main wire from the battery is what supply's the power for the fan, the little wire coming from terminal 86 work with the the wire to the thermostatic switch terminal 85. When the engine get up to temp that switch grounds out and the contacts inside the relay complete the circuit to send power to the fans. The 16 gauge wire running to the fuse block just turns the relay on and off, It draws all the power for the fan from the battery. When my fans kick on they do draw the power down for a sec but then the gauge goes back up to 14.5, so I would say you probably need a bigger alternator to keep up with the demand.
Brett
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Old 03-25-2004, 12:45 PM
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Another thought comes to mind - what is happening to you is that the fan is drawing most of it's load directly form the alternator which is a relatively big load, thus you engine is working harder to spin the alternator to supply the electrical power. However, one would expect the battery would supply the reserve power for the fan and your alternator would only marginally increase output to supplement the battery. Teh battery is a large capacity buffer that is intended to supply amps while maintaining constant voltage when a big load comes on line (starter, fan, air conditioning, etc.). The voltage drop (I would bet your volt meter is tapped into the alternator side of the system rather than the battery) and the alternator drag when the fan kicks on are identifying a wiring problem you have between the alternator and battery. It's like your battery is isolated from the rest of the system and the alternator is being forced to do all of the work. Check your battery cables and the heavy main lead (should be at least 10ga. I like to run two 10ga wires in parallel there) from the (starter/battery lead post?) to the fuse block.
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Old 03-25-2004, 01:05 PM
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My battery is in the trunk so the fan relays are connected to a terminal to which is also connected the alternator. When the fans come on I see the voltmeter go down then it picks up, no rpm change. The relays are protected with 18 ga. fusible links, each one powered individually.
Madelectrical advises the use of two relays for 16 inch and up electric fans. Taking power in the engine compartment also shortens the amount of load carrying cable.
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Old 03-25-2004, 01:56 PM
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Malc; your system is an example of what Horvath's should be. It doesn't matter where you take the power for the fan relay, nor where the battery is located relative to the fan & alternator as long as the battery and alternator are well connected. Yours obviously is. However, if there was some sort of resistance between your battery and alternator, you would likely see what he is seeing.
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