Anyone who has the Nelson harness and have or had problems with large draw on the Alt when A/C is on , lights flickering with A/C clutch cycle , Alt gage dropping when A/C clutch cycles , here is a diagram that will cure the problem .

I have a 2005 1500HD (3/4 so no e-fans) and did the 2005 fan install and Nelson harness , the Nelson harness is designed for LS1 or Flexlite fans and not the 2005 stock fans , so the harness does not work to well , but with this diagram the 2005 fans work great .

 

Second relay from the left - why?

 

Upstream or downstream of the fans , one relay acts as a converter so to speak , converts 12 volts (+) hot to a (-) ground trigger , the fan modes are, NOTE FOR 2005 FACTORY FANS , they draw alot of amps when both running on high speed . MAY NOT WORK FOR LS1 OR Flex-A-Lite FANS

1.No temp , no A/C no fans
2.No temp , A/C on 2 fans low
3.Temp , A/C on 2 fans low
4.Temp , no A/C 2 fans low
5.Exterme temp , no A/C 2 fans high
6.Extreme temp , A/C 2 fans high

I did not design this harness it was actually designed by RedHeartbeat , he used a diagram posted by Aklim on LS1truck.com .
This is designed for a 2005 PCM with the ability to have two PCM pins activate it , pin42 low temp and pin 33 high temp , one could use the high temp pin wire as a trigger , triggered by a high pressure switch or sending unit .

GM

 

I see. My understanding of pin 33 was incorrect.

 

Does it draw enough air through the condenser when the fans are on low to keep the a/c cold? I would like to keep the high speed from cycling all the time, but I want to make sure the a/c still works well in the 115* summers here....

 

To be honest I have not used the setup in hot weather yet , but the way the fans run are just the way a 05-06 1/2 ton work .
Had a freind use his 05 1/2 ton as a example of the way the fans needed to cycle and the modes I described is just the way the fans worked on his 05 1/2 ton .
Remember these are the 05 stock factory fans (34" radiator) and not the LS1 fans .
I live in Texas , so summers get hot here also .

GM

 

You can set this schematic up with the 05 fans, LS1 fans or flex-a-lite fans - you just need an '05+ computer in order to use pin 33.

 

Jesse mentioned something about enabling another pin when he did my tune. He said something about the A/C being wired from pin XX and the temps being wired from pin 42. I wonder if it's set up like you guys are describing. BTW, my truck is a 2004, Jesse put my tune on a BRAND NEW PCM(at my request), so I wonder if my PCM has the capability that the '05s do?

hmm....