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Old 03-04-2019, 02:12 PM   #1
PurdueSD
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Fan Relay —selection/wiring

I possibly want to use a factory 20A GM relay to power an electric fan. It was previously a tbi fuel pump relay. Is this a solid idea?

Could anyone help me interpret the relay diagram so i can figure out how to wire it up? Battery(+), fan power from fuse block. Ground from temp switch and fan(+) out is what i believe I need. Thanks in advance!
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Old 03-04-2019, 03:29 PM   #2
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Re: Fan Relay —selection/wiring

I see the wiring diagram embossed on the top of the relay, but am having a hard time making it out. You'll see two wires that power the solenoid. D and F on your diagram. A, B, and C are harder to make out. They are simply the three points of a single-pole double-throw switch.

If you look at the bottom side of the relay, beside the output pins, you'll see the same letters embossed beside each pin. Use a multi-meter to confirm continuity. D and F should be connected, and two of the others should be connected while in the off position.
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Old 03-04-2019, 04:10 PM   #3
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Re: Fan Relay —selection/wiring

A 20A relay to run a fan or two? That must not be a very HD fan to begin with-what is the fan from originally?
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Old 03-04-2019, 04:56 PM   #4
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Re: Fan Relay —selection/wiring

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Originally Posted by gmachinz View Post
A 20A relay to run a fan or two? That must not be a very HD fan to begin with-what is the fan from originally?

Just a 16" aftermarket fan 140W. So it should only pull around 10 to 11A. Am i looking at something wrong?

I have the relay and it matches another one on my firewall. It also already has a nice weather pak connection. And in my experience the OEM stuff is way better than much of the aftermarket stuff.

Fan i got from champion radiator... think its this one:
https://www.championradiators.com/cooling_fan_16_inch
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Old 03-04-2019, 05:01 PM   #5
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Re: Fan Relay —selection/wiring

Quote:
Originally Posted by kipps View Post
I see the wiring diagram embossed on the top of the relay, but am having a hard time making it out. You'll see two wires that power the solenoid. D and F on your diagram. A, B, and C are harder to make out. They are simply the three points of a single-pole double-throw switch.

If you look at the bottom side of the relay, beside the output pins, you'll see the same letters embossed beside each pin. Use a multi-meter to confirm continuity. D and F should be connected, and two of the others should be connected while in the off position.


I am getting some inconsistent advice.

Ok, so it was my understanding that:
E and D are the power + feeds

I think that leaves:

C- normally closed -not used for me
A- Normally open - power to fan

F - ground coming from a temp switch
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Old 03-04-2019, 06:33 PM   #6
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Re: Fan Relay —selection/wiring

I'm holding a '87 tbi fuel pump relay and connector. I intend to pick up two or three more at the pick-and-pull, to use for two fuel tanks and a headlight relay(operated with the key switch).

Assuming mine is the same as yours, which it looks like, it's not a weather pack, but is a metri-pack.

Looking in the bottom side, I see pins D and F are metri-pack 280 blades(2.8 mm wide). These being smaller, it stands to reason they are the signal wires coming in. It doesn't matter what's ground and what's hot between them, since they are simply either side of a small coil of wire. In the stock application, one of those pins was connected to ground, and the other to a switched hot through the TBI ECM.

The three large pins are labeled A, C, and E, and are metri-pack 640 blades(6.4 mm wide). These are the switched load. Your diagram is a little vague. My diagram was merely printed on the relay, and has long since rubbed off, along with the part number.

I attached a diagram from google that shows the correct wiring for this relay in the stock application. Note that E is normally connected to C. When 12 volts are applied across D and F, this moves E to A, leaving C disconnected.

Again, confirm these pins match up with the attached diagram using a ohm meter. I'll do so myself before installing them in my application just for peace of mind.
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Old 03-04-2019, 06:46 PM   #7
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Re: Fan Relay —selection/wiring

Re-reading your first post, the temp switch grounds out when it wants a fan to come on. Thus, D and E would be connected to the temp switch and an ignition hot. Which one is which doesn't matter. The reason for an ignition hot, is so the relay and fan shut off when the key is turned off.

A and E would be connected to a fused battery hot and to the fan hot. Again, the order doesn't matter. C would be ignored. The fan would be grounded through conventional methods.

A possible method of wiring A and E would allow for easy testing of the fan. The stock application does that for testing the fuel pump. Note that if 12 volts are applied to C while the relay is off, the attached fuel pump will run. This feature could be applied to your situation, though I doubt there's much point.

An unrelated but amusing sidenote:

Yesterday, I was tracing the stock 2010 wiring on a Tahoe fusebox/wiring harness/ECM that I picked up. It turns out the ECM on this LS engine sends two ground signals to three relays, which in turn, operate two fans. If A is grounded, fan #1 turns on full speed. If A and B are grounded, fan #1 and #2 operate in series, thus both are turning slow. If B is grounded, both are running in parallel, and thus turning full speed. It's amazing the gymnastics you can accomplish with five-pin relays.
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Old 03-04-2019, 06:53 PM   #8
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Re: Fan Relay —selection/wiring

I'm afraid I've muddied the waters more than I helped. Your planned connections in post #5 will work fine.
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Old 03-04-2019, 06:54 PM   #9
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Re: Fan Relay —selection/wiring

Yes D and F are both smaller... D on mine has a + sign also so, this would align with my theory....

E= + from battery (fusible link needed)
D= + with key on from fuse panel

A= +to fan -Normally open, closes when F supplies ground)
F = Ground from temp switch
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Old 03-04-2019, 06:57 PM   #10
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Re: Fan Relay —selection/wiring

Quote:
Originally Posted by kipps View Post
I'm afraid I've muddied the waters more than I helped. Your planned connections in post #5 will work fine.
No worries! Thanks for your input, i understand it better after talkingbit through
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Old 03-06-2019, 09:39 PM   #11
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Re: Fan Relay —selection/wiring

I tried a 16 inch fan on my 350 three core radiator without a shroud and it would not keep the temperature below boiling.
I also would not use smaller than a 40 amp relay.

Here's a diagram of wiring up a fan with a toggle override and a operating light if you wanted one. The grounded side of the temperature sensor would trigger the relay and the ignition switch would power the positive side of the coil. You would have to figure out the battery power and the fan power and the normally closed terminals, which I think you have done.

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Old 03-13-2019, 10:48 PM   #12
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Re: Fan Relay —selection/wiring

Should only will get your project burnt down..or at the least a cooked motor... how many amps does it draw.. no should here. There other relays to use that can handle a fan and be waterproof..
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