Coolant fan connection with LS3 and AC

[Mastertech5]

Reading through the A.C. wiring instructions it says to cut a green wire at the relay and crimp the blue wire from the A.C. harness and green ones together and reconnect the other end back to the relay wire. Does this green wire activate the relay or does it go to the coolant fan? My engine instructions say to connect the coolant fan wire directly to the fan wire in the FFR harness.
This question is directed to edwardb or anyone else running this engine/AC combination. Does there need to be a diode installed in the fan wire from the ECM so when the A.C. is turned on it doesn't back feed the ECM when it turns on the coolant fan for condenser efficiency?

[JimLev]

The fan should come on anytime the AC is on.
I used the wire from the ECU to control the fan however I added a PWM speed controller to control the fan speed at around 30% so my fan will run all the time to help blow heat out from under the hood. I’m not a fan of having the engine temp go up and down and having the fan switch on and off.
When the ECU decides that 30% fan speed isn’t enough the fan will then go to 100% speed. I’m controlling the fan via 2 parallel circuits.

[Mastertech5]

I see.
In the instructions it says to locate the white wire and crimp a ring terminal to ground. I find no white wire that the instructions are talking about. The only white wires are from the heater control module to the temp switch, the 2 going to the trinary switch and the one that goes to the compressor.

[Kbl7td]

Trinarys get way easier to understand when you look at what’s actually happening. The Trinary just provides ground to the fan once a certain pressure is reached, which cools the coils. So basically only 4 wires coming out of the Trinary, 1 hot in, 1 hot out that turns on power to the compressor when the Trinary decides a certain pressure is met. Then two grounds. One is always grounded. The other ground is led to your fans. This probably wasn’t what you were asking but I’m sure someone in the future will be wondering the same!

[edwardb]

Have done two A/C installations with the RF harness. One with a Coyote in my Coupe. The other with the LS3 in my truck. The Coyote was with the FF kit, so followed their directions. As it turned out, the LS3 with the Chevrolet Performance electronics pack is wired exactly the same way. The Coupe has been on the road for three seasons and it works the way its supposed to. The truck isn't done yet, but functionally also works properly. Rather than describe wire colors, etc. (which I find a bit confusing, I use the schematics...) I'll describe functionally how it should be hooked up.

The summary is that both fan wires are used and either can power the fan as needed. The LS3 fan wire, in your case, will power the fan on/off based on engine temperature and the settings in the PCM. The RF fan circuit will power the fan on/off based on the trinary switch and refrigerant pressure. What I did on both of mine is routed the engine electronics pack fan wire into the area of the front footbox and spliced it onto the RF fan wire that routes to the fan through the front harness. It's not critical where this happens. Just doesn't make sense to have both wires go all the way to the fan itself. For the RF fan circuit, one of the DK GRN-FAN THERMO SWITCH wires goes to the appropriate terminal on the trinary switch. You should have a schematic or instructions for each of the terminals. When the trinary switch closes, this wire goes to ground and the RF fan circuit is powered. I was a little unsure about having two wires potentially powering the fan (separately or both at the same time) and questioned FF tech support back when I was building the Coupe. They assured me this was OK, and it has been. No diodes or whatever are required. Both circuits have relays, so backfeeding isn't an issue. Hopefully this all makes sense.

[Mastertech5]

Yes it does. I like to understand how the circuits work and not just hook things up as described. It's been a long time since I have worked on AC circuits that the computer doesn't control everything by just using inputs from sensors. I am used to looking at flow chart style schematics called Valley Forge style that GM uses. Thanks for the info. The white wire that they want me to ground is still a puzzle though. It's the first picture on page 79 in the PDF A.C. instructions.

[edwardb]

...The white wire that they want me to ground is still a puzzle though. It's the first picture on page 79 in the PDF A.C. instructions.

I honestly don't know. Reviewed the instructions at that location and reminded myself again why I only used the schematic and not those color-by-color instructions that don't have any explanations. That "white wire to ground" instruction is in the context of the heater control valve. But the white wire there goes to the temp controller. It's definitely not a ground wire. They give you a piece of white wire to extend certain leads, and maybe somewhere that's what they're referring to. But I don't know. I wired mine exactly like the schematic and they both work.

[Mastertech5]

Well if there's no white to ground and you're works fine, that's good enough for me.

[edwardb]

Well if there's no white to ground and you're works fine, that's good enough for me.

Well, one last disclaimer. Again, I used the schematic to wire mine. Not the word descriptions. There are several grounds. Somewhere that white wire they're describing is grounded. It's just not the white wire in the previous paragraph. As a rule, I found the 90+ page A/C instructions very helpful and appreciated the detail. But when it came to the wiring, I just went to the last pages where the schematics are. I need to understand functionally what I'm doing. Not just wire one color to another. However you choose to use the instructions, check your work by following all the wires shown in the schematic. It's not that complicated. Good luck.