Question: LS3 fan control wire; power or ground?
 

I’m looking at purchasing the Entropy fan controller but I do not want to run their secondary temperature sensor. On my LS3 crate engine with the GMPP harness, does the single blue fan wire send 12 V or a ground signal? I’m sure. this has been covered in depth already but after numerous searches, it is evading me. Thanks!

The big fat blue wire is power. It comes from the fan relay in the fuse box. That relay is computer controlled.

You won’t get two speed fans if you don’t use their sensor.

Yeah, that's the downside. According to Frank at Entropy, unless you wire the yellow wire to a ground activation, or use their sensor, you won't get the "two speed" function...at least not when the high/low fan wires are joined in the GM fuse box. Bummer cuz I like their setup.

http://www.gm-efi.com/news/pcm-ncs-g...ctric-fan-kit/

Works like a charm

Thanks, Randy...I checked that out early on but was intimidated by the prospect of messing with the ECM. Also by the fact that that fuse box is a total PITA to try to open up! I don't own HP Tuners so would I have to send them my ECM? It's also my understanding that I'll need the AC bump harness as well. I like the fact that it's 100% integrated and all relays, fuses, etc. will by in the engine fuse box.
Any insight on getting to the inside of the fuse box as well as the ECM side would be most appreciated!

I purchased the Entropy LSX fan controller kit. Super easy to install. Plug and play essentially. Absolutely love the 2 speeds. I did not use the GMPP blue wire. I just capped it off. I'm also using their radiator.

Someone in your area has to have HP tuners and if so its really easy to upload. Opening up the fuse box is simple as well. Instructions in the kit were very easy to follow. I purchased the AC bump kit as well which instead of connecting the AC bump by the ecu just connect it to the wires you are already messing with when working with the dual fan kit. In in all it took me about 45 min to install and everything works OEM. This will clean up all of your wiring for your fans and you will love it.

Wish you were closer i would just help you out

Alrighty, pulled the trigger on the PCM of NC fan harness and AC bump kit setup. Spoke with them on the phone and they sent me their instructions to check out prior to ordering. Other than the fact that you have to splice into a couple of the ECM connectors (which scares the crap out of me) this should be a slick setup. Even at that, the instructions are very detailed about where to make the connections both inside the engine fuse box and the ECM connectors.

Randy, I appreciate your input on the matter and certainly the offer of help! One question I have for you is that, if I understood PCM correctly, there's no need to run a trinary switch with this setup since the ECM/fans get the signal to activate or speed up directly from the AC compressor itself, correct? If that's the case then that will further decrease the wiring in the front of the car.

Binary switch

All the wiring is inside the fuse box. You don’t need to touch any connectors. When you get the kit and your ready to start the wiring I will walk you thru it since I still have my instructions.

Bottom line is you have two wires going to the one relay. I think blue and green. You cut one and then reroute it to your new relay. You give that relay some power, fuse it, and add a line out. Now your fuse box has two line outs. The wire that you tap into for the AC bump you are already working with the new dual fan kit. Tap into it at the fuse box and some other wires. Trust me it’s really easy once you start messing with it.

When you get the kit just text me at 972-814-8824. Maybe when I have some free time I’ll dig my instructions out and just make a diagram for you