School me on relays

[rob249]

These are some ive been looking at, I could probably fit up to 10 inch fans, but ive been looking at 7-9 inch. Most seem to list ridiculously high cfm's.

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Since im not sure how much this will actually help my AC, im leaning towards the cheap fans.

 

[Orpedcrow]

Some of our trucks came with an auxiliary pusher fan in front of the condenser

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[Supercharged111]

You can use a diode to prevent back feeding, that's what I used on my 4hi setup on the 1500. If you were to swap in a 411 PCM, you could have the exact fan control you described.

 

[Orpedcrow]

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

Those are the numbers on a relay. You’ll also see 87a on a 5 pin relay. That’s the pin that the “switch” side of the relay rests on. You can ignore that pin in this instance.

 

[Orpedcrow]

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You can kinda see them in this picture. 85 and 86 are the terminals that activate the electromagnetic coil that pulls the switch between 87a and 87. 87a would be considered “normally closed” and 87 is “normally open”. The switch pivots on 30 sending the power from 30 to either 87a (when inactive) to 87 (when active). The main purpose of this type of relay is to allow you to use a low current source (small wire from a/c switch) to switch a higher current source. (Bigger wire from battery). If you were to just run a power wire from the battery to a toggle then to the fan, you’d have to have a high current wire running through the truck and also need a high current switch (these can get hot) then back out to the fan.

With a relay you can leave your high current stuff in the engine bay while also keeping the run shorter, then use a small wire with low current as a switch.

 

[rob249]

I was more wondering why those exact numbers. What signifigance does 87 have, why not 92, or 36, etc.

 

[Orpedcrow]

I was more wondering why those exact numbers. What signifigance does 87 have, why not 92, or 36, etc.

Oh. That I don’t know. It’s just what they’re all marked as. I guess it standardized. Almost all 4 and 5 pin SPST/SPDT relay is going to have the same numbers that corresponds with the same pins. Unless they’re manufacturer specific.

 

[TechNova]

DIN numbers and why they’re so helpful

What are those numbers? They’re called DIN-standard relay terminal numbers; DIN stands for Deutsches Institut für Normung (German Institute for Standards). Sometime around the middle of the last century, German cars began following DIN 72552, which is a numbering standard for automotive electrical terminals. DIN 72552 covers far more than just relays. It’s the reason nearly every ignition coil on a European car has the numbers “15” (power from ignition switch) and “1” (low voltage to distributor) on the two small terminals, and also why starter motors are labeled “15” and “30.” Perhaps it is most useful in describing, understanding, and troubleshooting relays since the function of a relay, the socket it sits in, and the wiring of that socket, can always be reduced to the DIN terminals.

Not all cars follow the DIN relay numbering standard—vintage British and American cars certainly don’t—but the standard was eventually adopted by virtually all automotive manufacturers. I doubt you’ll find a car built since the 1980s with a relay that doesn’t follow the DIN standard.

Here is the DIN standard numbering of the four terminals on every relay:

Terminal	Which Circuit?	Definition
86	Low current (control)	Relay coil + (power input)
85	Low current (control)	Relay coil – (ground)
30	High current (load)	From battery +
87	High current (load)	Output to device, normally open, pulled closed when coil is energized
87a	High current (load)	Output to other device, normally closed, pulled open when coil is energized

 

[Orpedcrow]

DIN numbers and why they’re so helpful

What are those numbers? They’re called DIN-standard relay terminal numbers; DIN stands for Deutsches Institut für Normung (German Institute for Standards). Sometime around the middle of the last century, German cars began following DIN 72552, which is a numbering standard for automotive electrical terminals. DIN 72552 covers far more than just relays. It’s the reason nearly every ignition coil on a European car has the numbers “15” (power from ignition switch) and “1” (low voltage to distributor) on the two small terminals, and also why starter motors are labeled “15” and “30.” Perhaps it is most useful in describing, understanding, and troubleshooting relays since the function of a relay, the socket it sits in, and the wiring of that socket, can always be reduced to the DIN terminals.

Not all cars follow the DIN relay numbering standard—vintage British and American cars certainly don’t—but the standard was eventually adopted by virtually all automotive manufacturers. I doubt you’ll find a car built since the 1980s with a relay that doesn’t follow the DIN standard.

Here is the DIN standard numbering of the four terminals on every relay:

Terminal	Which Circuit?	Definition
86	Low current (control)	Relay coil + (power input)
85	Low current (control)	Relay coil – (ground)
30	High current (load)	From battery +
87	High current (load)	Output to device, normally open, pulled closed when coil is energized
87a	High current (load)	Output to other device, normally closed, pulled open when coil is energized

That’s incredible. Thanks for sharing!

 

[Erik the Awful]

Here's my explanation of relays from another thread. https://www.gmt400.com/threads/best-place-to-get-power-for-driving-lights.61051/

...The standard auto relays work fine. There are two terminals on the low-amp control side, and three terminals on the high-amp load side. I've wired stuff up for years, but I still have to put on my reading glasses and carefully check the terminal numbers against the wiring diagram every time I wire something up. I have also run into relays that use the same socket, but the terminals are different! Always check your relay's diagram.

In the pic below, terminals 85 & 86 are your low-amperage control circuit. Your switch will be on this circuit and 18 gauge wire is perfect.
Terminals 30 and 87 are your high-amperage load circuit. I'd use 12 gauge wire here.
Terminal 87a is used when you want the relay to open a normally closed circuit, also 12 gauge in the circumstances you'd use it.
For fun, wire power to terminal 30, jump terminal 87a to terminal 85, and ground terminal 86. Congratulations! You've just made a buzzer from a relay.

Relays are not polarity sensitive, so it's up to you how to run power and ground. The standard is to use terminals 30 and 85 for (+) and 86, 87, and 87a as (-) even though the diagram below shows 86 as power and 85 as ground.

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I'd suggest running a single 12 ga wire through a 20a fuse to terminal 30 and a 3" 18 ga jumper wire from terminal 30 to terminal 85. Run from terminal 86 with 18 ga wire to your switch, and from the other side of the switch to ground. Run 18 ga wire from terminal 87 to your driving lights, and then ground the other side of the lights, and you're done.

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Your diagram shows a ground on your relay that doesn't exist.