1FastBrick

iTrader: (17)

Here is the PCM of NC harness instructions for the 99-02 truck.

vidan27

Thank you so much for the instructions. Mine is definitely not setup correct at all. I'm just hoping my harness is a pcmofnc.

Shady Rascal

My harness is from Nelson Performance. Everything does work properly. When the AC cycles on, the fans run at high speed. I tapped my green wire into the AC clutch wire by the alternator and the blue wire went to the ECM into the empty spot (42, 43 ? I can't remember).

vidan27

That is how mine is setup now. Only kicks fan 2 on high when the compressor clutch engages. So it's always cycling on and off.

00pooterSS

iTrader: (40)

Sounds like it's wired wrong to me.

Without going through the schematic I can't break it all down and without knowing what all you have exactly I can't either but I can simplify.

There are 3 relays for the fans. On low speed a relay is a pass through essentially to make the fans be wired in series. On high speed it uses two individual relays to make a paralleled wired setup and feed them both full voltage instead of having them share and split the voltage.

you have your a/c compressor wire triggering one relay and that's why the one fan comes on and off with the compressor

If the compressor cycles on and off a lot it's low on freon

Go through the wiring again and you should be left with two trigger wires triggering your relay pack. I like to use the OEM relay pack and fuse block to simplify all this and keep everything OEM dependable. The 05 and up fan relay/fuse module snaps right on to the side of the early 00's truck fuse box and makes for a really nice setup.

When you get it sorted and have two wires left one wire will trigger low speed fans and the other will trigger high speed.

Sorry for the dumbed down post, it's been 7 years since I did one of those fan conversions