3 Relay Automotive Cooling Fan Logic

Trying to demystify the 3 relay setup for hi/low speed fans. It's really not as hard as it looks.
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[@TheTruthBeToId]

Dude my head was fuming on trying to make this work like thing. THANK YOU for having my solution before my head exploded.

[@RustyWrenches]

You bet. It still bends my mind a little.

[@tuanas458]

87a is for use like(for example) day time running lights which are automatically on when you turn on your car. And obviously it turns off(of become low powered) once you switch to the main headbeams. You can leave 87a open and not hooked up to anything.

[@bhwjrproductions]

I’ve had this 3 fan relay setup on my car for a couple of years, it’s been on the road full time for the last few months and it’s working great. The wiring diagram I used I found online. My LS computer controls the fans and I have a manual over ride switch that I never finished connecting because the computer controls seems to be perfect. I still have to figure out how to get the AC to trigger the fans.

[@RustyWrenches]

I also thought about adding a manual override as well. Maybe someday. I'm really hoping the pressure switch will work with my setup so the ECM will control the fans for the ac. We will find out soon! Thanks for watching!

[@stevemullin7472]

85 is ground on any relay I've ever seen?

[@frankm8533]

Seems right Lol. I was never to good with wiring or circuit stuff I just never learned it right

[@RustyWrenches]

Thanks. It takes me a good bit of staring at it to quasi-understand it. It makes just enough sense to get myself in trouble 😀

[@dickmick5517]

I am not sure my fans are rated to run on reduced voltage? Right now my set up is the two relay style with one computer input for each fan. I do like the possibility of running them at a lower speed to reduce the noise. However, I have the same issue as Bruce. How to get the AC to trigger both fans. Right now I am considering using only the lower temperature computer input for one fan and the AC input for the other. The other possibility is to use the same circuit you outlined with the two inputs, one LS ECM and the other the AC. Thanks and looking forward to any AC solutions you may have.

[@RustyWrenches]

I'd call the fan manufacturer and ask. From what I have read, you can use a trinary switch to trigger both fans by wiring the trinary swith to both the green (fan 1) and blue (fan 2) wires. You will have to add a diode and resistor on that line so the ECM doesn't see it. I may talk a little bit about that in an upcoming video. I am adding these wires in just in case my pressure switch doesn't do what I want it to. There are a lot of way to do it, just depends on how you'd like it to work. Mine is going to let the ecm control both, both low and high speed via pressure sensor. I can program the ecm to turn the fans on/off at certain pressures in the a/c system, or so I am told haha. I'll find out soon.

[@dickmick5517]

@@RustyWrenches I plan on using both the ECM ground and the Vintage Air supplied ground on high speed fan relay. It it gets hot both fans come on and if the AIR is on they both come on. That should work don't you think?

[@RustyWrenches]

That should work.

[@dickmick5517]

So does the ECM keep the LOW Speed connection grounded when the HIGH SPEED is grounded? I assume so, then the fans will just slow down the when the system/computer drops out of High speed. I think I answered my own question but no one ever mentions this part of the system.

[@RustyWrenches]

Yes it does. On my truck, fan 1 come on at 202 and off at 196. Fan 2 on at 211 and off at 203. So fan 1 will run regardless of what fan 2 is doing until the temp sensor sees less than 196. It is tricky thinking about this stuff.

[@ibanez741852]

The fatal flaw shouldn't be a concern. If you have 12v on both sides of the fan it's an open circuit so current won't flow. There is no ground. If you touch 2 wires to positive and touch them together on the other end, nothing happens. Electricity is trying to take the shortest path to ground. Now if that first relay was shorted to criund before 30 and the second relay was not functioning it would turn the fan backwards but what are the odds lol Great video though!

[@RustyWrenches]

Fair point. Thanks for watching!

[@samisulaiman7967]

I have a Suburban 2012 and I want to make both of the fan run on high speed all time and I have 4 relays with 5 pins can you show me the diagram thanks in advance

[@RustyWrenches]

That’s a good question. I don’t have an answer on that. You might try calling Current Performance. I know they do a lot with tan wiring.

[@VideosByAl]

Interesting solution to noisy fans.

[@RustyWrenches]

It really is. I can't take credit for it, but it sure is going to be nice!