Working on.a friends truck... 03 Z71. He just put a set of electric fans and a nelson fan harness on last night. I've already turned fan 1 on at 100 degrees and fan 2 on at 170... I set both of the off temps to max value just for arguments sake to make sure that wasn't the problem. I have the off run time at 45 seconds for a cool down period after the truck is shut off...

the fans won't come on with the temp. Scanned all the way up to full temp but the fans never came on. Until... We turned the ignition off, 45 seconds AFTER the key was turned off lol...

The only thing we changed was the plugs on the harness to fit the fans he got. They're GM salvage yd fans. I don't think that would make it do what it is...

I'm gonna go back over the harness again today just to see. But they won't come on with the A/C or anything. What gives?

 

Which wire did you tap for the A/C wire? There are two green wires in there but that still wouldn't explain them not coming on at temp. Which configuration did you use in HPT, 1 fan, 2 fans, or Aux?

 

I tried 2 fan and aux both... Same results. Its an 03... Is it not pin 42 like the 99-02? That's what I was told and that's what the instructions said.

 

I believe all of them use pin 42 for fan 1 and pin 33 for fan 2....

 

The harness only came with one PCM pinout though....

 

Right, you have to run the other one to the green A/C clutch power.
Wirring them in this way will only allow the pcm to control one relay.
You can switch the a/c clutch relay around in the nelson harness and let the pcm command both fans. but you will need to supply the green wire that goes to the clutch harness with 12v fused key "on" power. then remove the ground for that relay and run it to the pcm....
I've done this and helped others do this on the 04 and 05 trucks. It "should" work for the 03's too.
A easy test would be to use a dvom to check resistence between pin 33 and ground by command the pcm to turn on the fans with hptuner controls.

 

hmm. Dont waste your time after you get them set up with turning them on that early. it runs at the thermostat regardless.

 

HUH?

Ben, have you checked to see if the pin from the PCM is grounding?

 

Well there's already a purple wire in pin 33. We will try testing the harness I suppose. I just went in and took the 45 second over run time off and still getting the same.

I plan on changing the fans both to 180... I just dropped the temps so low to see if they would come on independantly like they're supposed to. I never thought a set of fans would kick my *** this bad. Lol I've put on probably a dozen sets hahaha...

 

That wire goes to the auto-recirculate function of your heater/AC.... I have read that some guys just splice into that... That is why most people use pin 42 on the other connector... In EFILive there is a setting on what you use that pin out for, either efans or auto recirculate... I have mine setup to use both pin 42 and 33...