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I have a LC9/4L60E combo with a PacificFab wiring harness that I'm trying to add my Vintage Air heat/AC system to. I'm running a Ron Davis radiator with dual Spal fans and need to tie my trinary switch to. Wiring for the trinary says to tie into the fan relay unit, but I have 2 fan relay units in the engine power supply box. Ill attach photos...
I assume since my wiring only came with the two fan relays, I have either one fan running full or both, and not a high low function?
Fans on with the motor running doesn't sound too loud so I'm good with just the two relays, this is an off-road rig after all.
I found this wiring diagram, attached, which I think I can just tie into the one relay (terminal 85) for the trinary and be good? Any and all opinions welcome!
The way those fans work is, there are 3 "modes": one wherein both motors are fed 12V on one side and ground on the other, which causes them both to run at full speed; another wherein only one motor receives power that way, such that the other does nothing, while the one runs full speed; and last but not least, where the 2 motors are in series, such that 12V is applied to the + terminal of one, then that one's "ground" wire is connected to the + terminal of the other, and the other's ground wire is ... grounded. That last, runs both motors at some lower speed, because in effect, each one has 6V applied to it instead of 12V.
In many of the GM trucks, there is little or no interface DIRECTLY between the fan wiring, and the AC system. This is because the ECM knows AT ALL TIMES what the AC system is doing, since it commands it; and chooses the fan mode accordingly.
If it was my vehicle, I would eliminate the "AC thermo switch", the "trinary switch" (I must admit, that's about the weirdest concept for such a thing I've come across all day in a day of weird concepts), the "fan temp switch", and the "manual override switch". In a word, get a copy of a truck FSM (a DVD is available for around $15), and duplicate that in your Cheeeeep. You've got all sorts of complications and whatnot that aren't necessary and only serve to overly complicate something that's pretty simple and reliable and BULLETPROOF as it came. All those bizarre "improvements" aren't really gaining you anything except adding more potential points of failure. That includes simplifying the compressor control signal. All of that "manual override" kind of stuff is just a waste of effort and a subtle scattering of shiny things off to the side of the path to divert those who are easily distracted and who have a short attention span. Don't be one of "those" people.
Good info thanks! I'm hoping, I have scenario "three" where my fans both run at low and high with just the 2 relays... Ill check more into that to confirm.
The diagram had a bunch of additional items that my rig does not and was just a diagram I found online while looking for a solution. I would not be including a manual override, and I do not believe my harness has a "traditional" fan temp switch on the motor. The only temp sending unit like that I see goes to my instrument cluster only.
The AC thermo switch, is just a fancy way to say my AC switch on my dash to turn on the AC. Everything I read indicates I need a binary switch for a mechanical fan and a trinary switch is I have electric. Ill call Vintage Air tomorrow and see if I can get some further clarification on a vortec motor with a ECU.
Anyone else have an opinion of this? Im welcome to any suggestions. Any way to see how my fans operate besides just running the engine and seeing what fans come on? Currently have the heater core out...
I would look into running an f body tune and a pressure sensor. That way you can turn the fans and compressor on by refrigerant pressure and coolant temp. Run the compressor call wire through alow side switch and your all good.
I think straying from the GM factory design is a bad idea. Any LS PCM can run electric fans, even the early truck PCMs; you just have to enable it in the tune. GM engineers spent countless hours to make the two-speed fan setup work reliably.
When you start trying to control the fans/ AC system with auxiliary sensors and switches, it opens the door to all kinds of problems.
For example, in that diagram, I don't see any AC Request Signal wire going to the PCM. Thus, the PCM doesn't "know" that the AC compressor has been switched on, and the engine speed will bog down at idle. I have seen guys do this very thing before, and usually they just turn up the idle speed so that it doesn't stall out when they are sitting at a light with the AC on.
But now their idle speed is too high when the AC is off, and the car is trying to run away from a stop.
This is around the time that they bring it to me, asking what I can do to fix the situation.
When I ask "Why didn't you just use the factory setup," they look down, scratch their necks, say:
"Uh, well, you see, I bought this kit..."
AC fan activation output of the trinary switch will connect to ground activation point of the fan relays (assuming you have PCM fan control with ground activation control)) will have to connect to the low speed and high speed fan control to activate high speed fan operation (if youre using F-Body series/parallel fan relay setup). The fans will operate off the preset pressure of the trinary switch during AC operation.
11-12-2023, 08:30 PM
Wiring a trinary switch to LC9 relays?? 
