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Discussion Starter · #1 ·
A company called PCM of NC makes and sells a dual fan harness kit that allows the GMPP ECM to operate a pair of cooling fans in either low speed or high speed, depending on demand. The ECM is factory programmed to operate just one fan at either on or off, but it has the capability to operate two fans in hi or low, that capability is just turned off in the software. To complete the installation, a tuner pro will need to go inside the ECM software and enable that feature, as well as set on/off temp settings. The great thing about this kit is that it taps in to the capability that already exists in your engine's ECM and fuse/relay panel, instead of having to add on another product to control the fans, which means more complexity, and more wiring to deal with, and more wiring to hide.

PCM of NC also offers another harness kit that works in unison with the first kit, for air conditioned cars. When the AC compressor is kicked on, the harness turns the fans to either high speed, or low speed, depending on how you want it set up initially.

I just finished installing both of these harness kits, and even though I'm not super comfortable doing wiring, I have to say that it wasn't super difficult. You just need to be brave enough to try.
 

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Thanks for sharing! I believe I have the same GM (495 HP), LS3 as you.
(less the after-market performance stuff)
Sounds like this would definitely benefit me as well!
Thanks!
 

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Discussion Starter · #5 · (Edited)
Here's the dual fan mod. PCM of NC GMPP Fan Harness Kit - Seamless Operation

Here's the a//c mod. Hot Rod A/C Fan Speed Bump Circuit (pcmofnc.com)

I bought and installed these also, but have yet to run/test them. I found that installing the dual fan terminals in the relay box to be a bit tricky but ultimately succeeded. The wiring on the bottom side of the relay box is a rat's nest, and I had difficulty getting one of the terminals to latch at first.
Rick, I had a devil of a time pushing one of the terminals into position on the fuse panel. It would go in most of the way, but not enough to catch. I had to actually to lightly hammer it into position. I though that maybe there was some mold flash in that location. All the other terminals went in easily, except that one.

Rick, did you choose to cut the yellow jumper on the AC kit? I couldn't decide if I wanted to or not, so I left it alone.
 
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