I have the Nelson Harness and I reccomend either putting the Higspeed Mode a manual switch or Wiring it so highspeed can be turned on by both the AC/PCM and a Manual switch...

The reason i say a manual switch is because in stop an go traffic the fans won't be on high unless the AC is on, i don't run my AC much so by doing this my Engine temps stay right at 179-185 degrees in even the worse traffic.

Now do rmember that if you only wire a manual switch for highsped you NEED to turn the fans on to high speed if you run the AC... I am working on rewiring the harness with a Double through relay to run both Manual and AC control for the fans, I am going to the surplus store this weekendto look for a relay.

 

If you hook up pin 33, you can program the hi speed fans to come on 5 degrees above the lo speed temps to keep it cool and drop the a/c pressure turn it on earlier and then you don't need a manual switch. I rewired the Nelson 3 relay harness to work on pin 33 and it works like factory. Works on 03 and later.

 

To run a (-) trigger on the 3rd relay (the high speed circuit in the diagram I have) you just need to swap the +/- on the trigger side of the relay (NOT on the load side).

However, since I have HPT, doesn't fan 1 turn it on at low speed and fan 2 setting turn on the high speed???

Which wire is the AC compressor wire? That's the one I really want since I don't have another pin to add to the factory harness. All I want to do is have the fans come on high with the AC only.

 

According to this thread, yep it is possible to control them like the 05+ trucks do
BigRedExpress99 got it to work
https://www.performancetrucks.net/fo...blowing+relays

and here

http://forum.efilive.com/showthread....highlight=efan

PN# for the GM relay setup 15216055

 

YES, hptuners guys please chime in on that thread and tell them you want this feature. even if you don't. lol it would be nice to have but they put it on the back burner because not too many people want it.

 

and its the solid green wire under the a/c compressor relay on the fuse box. not the green white. the green/white is looking for a ground and if you hook up to that one you will cause the compressor to stay on ALL the time. i know, i did it. i went by the wrong diagram.

 

Thanks, I ended up finding it with a volt-ohm meter. I didn't like the way it comes on every time the compressor kicks in (the idle would bog/surge EVERY time in drive or neutral), so I reqired the relays to look for ground and will get another pin for the ECU's high speed trigger. That way it's wired right just in case HPT gives us those other controls.

 

yeah i'm going to order the factory harness for mine. these truck fans keep burning up the ls1 fan harness relays. and it sucks in the summer because the a/c doesn't work very good at idle.

 

Am I understanding this correctly, if I get a EFI live I will able set all these settings as I want. Note: I have a pcm tune from nelson.

 

All of those and about 5,000 more.