School me on relays

[rob249]

I going to test some "helper" fans for my AC, get some more idle performance, just not sure what type of relay I need for this setup. I'd like to have the fans come on only when the AC is running and I have a dash switch activated. So I suppose I need a relay with two inputs, If thats the correct way to say it. Ive wired electric fans on a different car with a relay kit that operated off a probe that slid into the radiator, so just one input would turn the fans on.

I havent purchased fans yet, but im looking at dual 8" fans, and all ive looked at pull between 5 and 7 amps each. Fans will be mounted as pushers in front of the condensor.

I am going to replace my 105amp (CS144?) alternator with the optional 124amp, which will hopefully give me enough idle amperage to run these fans.

My AC runs ice cold when moving, it just can't cool my 2 dr Yukon at idle. It was 116F today at my house.

Here is a diagram of what id like to do, thanks.

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[kennythewelder]

I used 3 relays on my set up, and here's why. 1 relay for each fan. That way, each fan has its own relay, so not only can they be controlled separately, but they also have there own supply from the battery. If you loose 1 fan, at least you have the other fan, as backup. The 3ed relay, you need so that the AC compressor will not turn on, when the fans do. So, I tied the 3ed relay, into the AC clutch, and that relay feeds the supply wires for both of the other relays. When the AC, activates the 3ed relay, that activates the positive supply, for the other 2 relays. When the AC is off, there is no way for the fans to back feed the AC clutch.

 

[rob249]

These fans are in addition to the clutch fan, the electric fans will only be used as needed, and only when the AC compressor is running. Dont understand why i would need 3 relays, what am I missing here?

 

[kennythewelder]

Well, you can get away with only 2 relays, depending on how big, and how much draw the fans pull. The reason you need at least 2 relays, is BC you don't want you AC to engage, every time, your fans come on, unless the only thing the electric fans will do, is come on, only with the AC system.

 

[kennythewelder]

Well, you can get away with only 2 relays, depending on how big, and how much draw the fans pull. The reason you need at least 2 relays, is BC you don't want you AC to engage, every time, your fans come on.

 

[rob249]

Thats exactly what i want, only when the AC is running. I want to turn them off at speed as well, hence the switch.

 

[Orpedcrow]

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Let me know if this doesn’t make sense

 

[rob249]

I think I get it. Power from AC compressor to dash switch to relay. And fuse between battery and relay instead of after relay.

 

[rob249]

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Do I need two relays?

Edit; thanks for laying out what each number means on the relay, why #85, 86, 30, 87.

 

[Orpedcrow]

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Do I need two relays?

I would use 2, 5-7a seems inaccurate and awfully small for a fan that’s big enough for a condenser.
Also you’ll want your fuse within 12” of the battery.