Trinary Switch Integration with Dual Fans

[MDPotter]

Posting this for anyone that has a Gen 3 or 4 LS engine, Vintage Air, and dual electric fans.

When it came time to wire up my dual fans, I did a lot of research. By recommendation of a few members, I decided to run 2-speed fans. When I say 2-speed, that means both fans running half speed (in series, 6V) or full speed (in parallel, 12V). This way, the fans are quieter and they pull air evenly across the radiator like most modern day dual fan setups in factory vehicles. This isn't too hard, GM has a schematic for it that involves three relays. This gets a little more complicated is when you need to integrate a trinary switch from Vintage Air. Gen 3 and 4 PCM's supply a ground signal to the fan relays in order to turn them on and off. Conveniently, a trinary switch closes when line pressure reaches 254 psi and also provides a ground signal.

Going back to the GM PCM function (specifically the 3-relay schematic) - typically, when coolant temp reaches 195, a ground is sent via the "low speed" green wire and both fans run in series (half speed). When coolant reaches 205, a ground is sent via the "high speed" blue wire and both fans run in parallel (full speed). So when your A/C line pressure reaches 254 psi, you want both fans to be running full speed. It's not as simple as tapping into the correct wire of the GM diagram to turn on both fans full speed though. This is because the PCM runs diagnostics and it will see a faulty ground in that blue wire when the trinary switch closes and will then turn on the check engine light. To avoid this, you have to install a resistor and a diode on the blue wire that connects to the trinary switch. Credit to user prodjay1 for this. Using a resistor and a diode will only allow current to flow one way and will keep the PCM happy (or unaware of that other wire).

This all sounds great and in theory would work, but not all fans are two-speed. Sure, you can run a fan at 6V or 12V and it will work, but the fan may not be designed for that. In my instance, Spal fans are not designed to be ran half speed and will "prematurely wear out" according to Spal. So I found a wiring diagram for a 2-relay setup from Speartech which is based on Gen 3 and 4 engines. I then added the trinary switch, resistor, and diode to the diagram. I wired this up last weekend and here is the sequence of operation: Coolant temp reaches 195, fan #1 comes on full speed. Coolant temp reaches 205, fan #2 comes on full speed (fan #1 remains running). Trinary switch closes, fan #2 comes on full speed. So the PCM and Vintage Air are happy and both have control over fan #2. For the ignition source, I had not used the electric fan circuit from my American Autowire chassis harness and it is a "key on" ignition source so it worked perfect to utilize this formerly unused circuit.

Now, the trinary switch has no control over fan #1. If you want to take this a step further, you can tie it into fan #1 as well. But the likelihood of the A/C line pressure reaching 254 psi prior to the coolant temp reaching 195 is pretty unlikely.

[rodstored-72]

mdpotter,
Thank you for sharing this. I am wanting to do this on my same setup (which you have graciously answered questions for me already) I am looking to do this with my setup as well. I have talked to a rep. and he indicated that for my needs I should be able to stay with the binary switch in my sure-fit system. I indicated to him that I was going to be running a '13 LS stock motor. I ran a trianary switch in my '72, but the fans were wired on a stand alone setup. I am trying to get the engine wired now and then I will work on periphreals like fans and the A.C. system.

thanks!!

[derotoreut]

So I've had a few discussions with you on this subject through other's build threads and I'm glad you published this. I'm hoping you will be able to help me clear this up with my current build (build thread link below). I am confused by this and want to be sure I get it right. I'm doing a 5.3/4l60e LM7 swap.

My harness was built by Tilden Motorsports and includes two fan relays. I'm running Vintage Air's Gen IV system with trinary switch.

Here is my PCM and auxiliary relay/fuse box that contains my fan relays.



Fan-1 relay is on left; Fan-2 relay on right. Each has a green 30 amp fuse. Note: I think they had one relay in backwards, so I flipped it over (hope I'm right).





This is the back of Fan-1 relay. The large dark blue wire is the fan+ hot and the small blue wire is the trigger wire. My harness builder told me just to tap into the small blue trigger wire and run a wire to the trinary switch.



So I tapped into that small blue wire and came out with a purple color wire that I ran to the VA trinary switch (blue wire).


So I think all of my wiring is the same as what you show (other than resistor & diode). I want to be sure. One of the black/green wires at the trinary comes from my VA system (blue wire) labeled trinary, which I believe comes from the VA relay.

So is this wrong? Am I going to have a problem?

[derotoreut]

So here is part-2 of my wiring dilemma. I found this trinary wiring thread a while back and I don't really understand what they're doing and if this is the proper way to wire. It seems like they're using another relay? Help is appreciated to understand this.

Trinary wiring-1.pdf

Trinary wiring-2.pdf

[MDPotter]

You've got it right, you just need to add the resistor and diode on the blue wire going to the trinary switch. The diagram you posted is missing some info and shows something weird about pin 87, but other than that it's the same. The other PDF you posted where clinebarger mentions the PCM throwing codes is correct, that is why we install the resistor and diode so the PCM can't see this wire.

[derotoreut]

So that wiring diagram that I posted is all part of Clinebarger's thread. I didn't understand that wiring diagram. It looks like there is a relay with pin 87 feeding into the fan relay. Could this be a way around from having to use a resistor and diode?

Can you show me how you installed your diode and resistor? Do you have any pictures? I will have to cut into my wiring to install this. I have no room to install them in my cab without doing some work. Can they be installed outside of the cab any way? This is all new to me.

Also can you confirm that the green wire in your posted wiring diagram is the blue wire in Vintage Air's Gen IV connection instruction?

[MDPotter]

Originally Posted by derotoreut

So that wiring diagram that I posted is all part of Clinebarger's thread. I didn't understand that wiring diagram. It looks like there is a relay with pin 87 feeding into the fan relay. Could this be a way around from having to use a resistor and diode?

Can you show me how you installed your diode and resistor? Do you have any pictures? I will have to cut into my wiring to install this. I have no room to install them in my cab without doing some work. Can they be installed outside of the cab any way? This is all new to me.

Also can you confirm that the green wire in your posted wiring diagram is the blue wire in Vintage Air's Gen IV connection instruction?

That diagram from Clinebarger has everything wired correctly, but it doesn't incorporate the PCM fan trigger wires. The way it's wired doesn't take away the need for the resistor and diode.

Here is a picture of the backside of my fuse/relay block. The relay with two blacks and two reds is my fuel pump, ignore that. You'll see that instead of stripping a small section of insulation from the PCM blue wire going to 86 and tying onto it with the trinary switch blue wire, I put both wires on the same connector that the relay plugs into - just a little cleaner that way. I don't see a reason why you would have to put the resistor and diode right next to the fuse block, they just need to be between the relay and the trinary switch. You'll also see that instead of running two separate pink ignition wires to pin 85, I put two wires on one of the relay connectors and then jumpered over to the other relay. As far as how to install the resistor and diode, I soldered the lead of the resistor and the diode together, then wire to the other side of the resistor and the other side of the diode. Don't overthink it. Just make sure the resistor and diode are in the right order and that the diode is pointing the correct way. Once you have it all connected, you can test by touching the blue wire that leads to the trinary switch to a ground source (with the key on) and fan #2 should come on. Once you start it, you shouldn't have any check engine lights either which means the resistor and diode are doing what they're supposed to do.

The green wire in my diagram (running to pin 86 on fan #1) is the green trigger wire from the PCM. Are you looking at the green/black wire coming out of the trinary switch? The green/black that run to the compressor and A/C switch have nothing to do with the relays, they are part of the Vintage Air system only.

[87chevy.com]

Otjer option you simply install the factory high side pressure sensor and wire the 3 wires to ecu and no need for resistors or anything... then operates like factory

[MDPotter]

Originally Posted by 87chevy.com

Otjer option you simply install the factory high side pressure sensor and wire the 3 wires to ecu and no need for resistors or anything... then operates like factory

I've seen this mentioned too, but in my opinion it's not a good idea since it basically cuts the trinary switch out of the system. The trinary switch is a Vintage Air component and that component is designed to work with their system. If you're running all the components of a GM system, then yes, it would be prudent to use the GM pressure sensor.

[derotoreut]

Originally Posted by 87chevy.com

Otjer option you simply install the factory high side pressure sensor and wire the 3 wires to ecu and no need for resistors or anything... then operates like factory

Do you mean some sensor in lieu of the trinary switch? Can you be more specific on the wiring to the PCM?

[87chevy.com]

Originally Posted by derotoreut

Do you mean some sensor in lieu of the trinary switch? Can you be more specific on the wiring to the PCM?

A low psi sensor on the low side and the high psi sensor on the high side hose is all thats needed to make the system operate like stock with all the safe guards in place .
Clint

[MDPotter]

Originally Posted by 87chevy.com

A low psi sensor on the low side and the high psi sensor on the high side hose is all thats needed to make the system operate like stock with all the safe guards in place .
Clint

Can you post a thread about this with details? The intent with my thread is to explain how to integrate the Vintage Air trinary switch with the LS Gen 3 or 4.

[87chevy.com]

Originally Posted by MDPotter

Can you post a thread about this with details? The intent with my thread is to explain how to integrate the Vintage Air trinary switch with the LS Gen 3 or 4.

Sure, lets be specific. What year is the harness/ecu.

[MDPotter]

Originally Posted by 87chevy.com

Sure, lets be specific. What year is the harness/ecu.

How about a new thread in the LSx forum with an introduction to the concept of this setup. Then people can chime in with specific info for their application and detailed wiring diagrams can be posted from there. This thread has already gone far enough off course.

[derotoreut]

So I was thinking about how to wire for both fans to come on with the trinary switch and came up with this drawing. The diode arrows point in the direction of current flow, so isn't yours backward? Doesn't the flow need to go from the trinary switch to the relay in order to trigger the fan? also, then wouldn't you need a diode at the PCM too? Also can you explain the need for the resistor?

[dayj1]

Originally Posted by derotoreut

The diode arrows point in the direction of current flow, so isn't yours backward?

No, his diagram is correct. The cathode (negative) side of the diode is the banded end. In your diagram you have the cathode connected to 12 volts (through the relay coils). The PCM and/or the trinary switch provides ground to enable the fans and should be connected to the cathode side of the diode.

Originally Posted by derotoreut

Doesn't the flow need to go from the trinary switch to the relay in order to trigger the fan?

The trinary switch provides ground to the relay (and so does the PCM).

Originally Posted by derotoreut

also, then wouldn't you need a diode at the PCM too?

No. See below.

Originally Posted by derotoreut

Also can you explain the need for the resistor?

Like many microcontrollers, the PCM can switch input and output functions on a single pin. While we generally think of the fan signal as an output from the PCM, it also uses it as an input when the fans are not on to sense 12 volts and verify integrity of the fan control circuit (the relay coils basically act as pullup resistors in this scenario). The problem is when the trinary supplies ground and the PCM decides to run a check. It doesn't know anything about the trinary switch and assumes that there is a problem with the fan control circuit. It stores the fault, turns on the check engine light, and turns both fans on (hi speed cooling). The resistors are in the original poster's diagram to fool the PCM into thinking that it "sees" the 12 volts via the relay coils even when the trinary switch has the fans running. This is also why you don't add additional diodes on the control lines from the PCM. It will block the signal from the diagnostic check.

[MDPotter]

dayj1 beat me to it, but everything he said is correct. He is the original source of this approach. Sorry, I was a little off on your username.

Just to clarify - at first I thought the diode was backwards so I flipped it around and hooked everything up and it didn't work. Flipped it around the way I have it drawn and it worked. Electricity always looks for the quickest way to ground, so it has to flow through the trinary switch to the ground source on the other side, in the direction of the arrow.

[1971Stepside]

Otjer option you simply install the factory high side pressure sensor and wire the 3 wires to ecu and no need for resistors or anything... then operates like factory

VA has you use a binary switch and not a trinary if you use this setup. This is what I am doing on mine so the PCM controls the idle speed when the compressor kicks in. Seemed much more simple for me to do it this way, but I think it is whatever works best for you. I have a lot of wiring to go, so we will see how it all works. MD and Beaterku are my go to wiring guys

[SilverGT3RS]

Originally Posted by 87chevy.com

A low psi sensor on the low side and the high psi sensor on the high side hose is all thats needed to make the system operate like stock with all the safe guards in place .
Clint

I'd definitely love to see a thread about this. I'm running a Classic Air system with a 2003 6.0 LS swap. The techs at CA told me you can use the ecu and/or the trinary switch to cycle the fans.

I had an outfit in NC build a factory style relay set that comes already terminated to tie into the factory PCM, and the PCM is used to turn the fans on and off.

[Cmillwheels]

MDPotter and dayj1 thank you for your expertise in this matter! I’m currently in the middle of a gen III transplant with vintage air in my 68 C10 and was trying to figure this exact issue out, you guys saved me tons of heartburn!!

I have the diode and resistor and will be wiring this part of my build up today.

Thanks again you guys.

[kglowacky]

I like your relay box where did you get it?

[MDPotter]

Originally Posted by kglowacky

I like your relay box where did you get it?

If you're talking about mine, I got it on Amazon: https://www.amazon.com/ONLINE-LED-ST...5-4be35d7258cc

derotoreut's appears to be the Bussman center which is a notch above mine.

[kglowacky]

they both will work for me Thanks

[derotoreut]

My Bussmann came from my harness builder. I did not do my own LS harness.

[MalibuSSwagon]

This post answers some questions I had about integrating the Vintage air kit I just ordered with my LS setup, thanks.