So I have been running the same harness for the past three years and now my truck will over heat with the a/c on sitting still. Seems as there is only one fan that comes on high and the other shuts off when both pins are grounded. Without the a/c on both fans will come on low. All relays will click like they should when you put power to them. Fans are wired with three relays like the 05 fans and run of both pins.

 

Never mind tore my harness apart and found a wire came apart on the low speed relay

 

My suggestion was going to be check a relay. Glad you found it.

 

what harness are you using? only 1 of my fans come on high also...been like that since i bought it...

 

I am using one I made bout 4 years ago.right? Im in gonzales.if you want me to look at it for ya. It is all fresh on my mind how they work. You did have the pcm programmed for both pins right or are you using the ac comp wire to trigger high?

 

A/C comp wire... pin 42. since the day i put it in, it only kicked 1 fan on high, never 2. i was having a problem burning up the A/C relay for a while until i changed where the T tap went and havent had a problem since. yeah when i get time, id be willing to meet up and let you look over it. i'll buy ya lunch for your time.

 

That's cool pm me when you get ready. Any reason to not let the pcm control the fan instead of the ac comp or did you just never have the tune set up that way?