[QUOTE=2002C5COUPE]So, i guess when i order my harness i will just make sure they wire it to where i can use pin 33 as well. hopefully the place i get it tuned will know how to set it up to run the 2 pin activation set up.

Yes, ask for the high fan "to ground" wiring for pin 33 and extra pcm pins in case you bend one like I did. If you are putting the fans in your 03 you might want to make sure pin 33 is empty and is not used for a/c recirculate. I looked at a stock 2003 4.8L file and it was setup for "Fan #2 Control". Once you have it hooked up all he has to do is turn them on and set it up for your thermostat settings. BTW factory settings are set on at 226, off at 219 w/stock thermostat. You might want to lower that some to keep it cooler. I'm sure he will have some suggestions. Hope this helps.

Ron

 

[QUOTE=RWC]
hey thanks for taking a look at that for me! i wasn't sure if my PCM would be able to control the 2 fans like that. That info helps out a whole lot!

Could the voltage drop be in anyway associated with the source of ground, such as using the a/c clutch pwr vs. pin 33?

 

i noticed it for sure. i upgraded to a 200 amp alt, optima yella top, and i did the big 3)1/0 gauge power and ground replacing all the stock cable and 4 gauge alt wire to the 1/0 gauge. i never see below 14 volts now

 

How is the 200amp alt at idle? Or should i say how was it when it ran. JFWY. I heard they have a hard time at low rpms. Also what brand is it?

 

I also have another question. Is everyone having this problem with ls1 fan or just 05 fans? Thanks

 

im using 05 fans, m ine idles at over 14 volts. the alt is a stcok looking 145 amp that been boosted to push 200 .doign the grounds/ and battery cable upgrade is just as goos as the alt itself. imo a new battery isnt needed but the big 3 alt is ( unless you have a 145 amp alt stock) they should be ok.

 

[QUOTE=2002C5COUPE]
I don't think so. I believe the reason the factory setup works better is the pcm seems to have the fans running on low speed before it turns them on high, and the bigger alternator helps. They would have a lot less current draw starting at half speed vs starting from zero. Low speed puts them in series (~6V each), high speed puts both fans to full voltage. They would draw a LOT more current if you were starting them both from zero, but only till they got up to speed. THAT will make the lights dim when the high speed fans come on together with the a/c compressor as most aftermarket fan harness have them do. The factory setup runs the fans on low a lot of the time even when the a/c is on. Only high ECT or high freon pressure turns them on high speed.

 

That was a really good posting you have regarding the factory E fans programmed to come on at slow/high speeds, my truck does exactly what you describe you can hear the massive kick the dual fans make from a dead stop to full blast and watch the voltage drop then come back up. So is there a way to correct this, I tried the better wires, I have a 145 A alternator, I still have the problem. My harness and programming is from PCM4less.com I didn't really follow what you said you did to yours to get it to work like you wanted. Mine came with no AC trigger at all, which I had to use a relay for the positive trigger wire the harness had to get the stock truck harness ac trigger wire to work with it since the stock trigger wire is a ground?

 

i have a 05 and i dont have any problem but it doese go from 13.8 to 14.4 and back and forth but i believe that is just because it takes a sec to kick up the alt

 

It looks like all the 05 trucks came with 145A alternators, so that should be enough or at least GM seems to think so. I don't know what year truck you have but I looked at a few files and up to 02, pin 33 is set to "Auto Recirculation" and 03 and later it is set to "Fan #2 Control". In theory, 03 and later should be able to control high fan speed by grounding pin 33 and be programmed just like the 05's. You would need to check first to make sure pin 33 is empty as it was on my 05HD. If so, just setup your high speed relay to operate when grounded instead of when 12V is applied. It takes a 3 relay setup to do the "series-parallel" fan control. I don't know about PCM4less but I know the Nelson harness is 3 relays and most of them are wired to turn on the high speed relay with the a/c compressor using that as the 12V source. I modified mine by tapped into another relays 12V source to power the high relay full time and wired the other switch leg to pin 33 (ground) to turn it on. If you need a wiring diagram, "searching" should come up with one. Then program the pcm with your settings as unfortunately it is not setup to work from the factory. Hope this clears it up for you.