2000 Silverado E fan tuning
 

I have searched and searched and cannot find anything to help me out. The issue is when I turn on my cab fan (blower motor) the passenger side E fan kicks on then immediately off. It does this every 30 seconds or so. I have changed setting in the tune to every combination it seems. The best I have gotten so far is with it in AC re circulation and and analog cycling. I go all the way on to 4 on the cab fan without the surging. Go to 5 and it starts again. This issue also happens when i engage the AC. As soon as i hit the button my voltage drops to around 13v and the passenger fan kicks on then off and my voltage stays good. Of course with this happening i do not have AC until i get up to speed and start cruising. This also happens when i drive as well. Its worse at stoplights. Should the fans come on with the blower motor? I have also tried swapping in a junkyard 130 Amp alternator over my 105 to see if that was the problem. Didn't change a thing. other than 1/10 of a volt higher. I have added 2 extra 4 gauge grounds also. I bought the truck with the fans installed. It has an unknown brand aftermarket harness that goes to the PCM, has 3 relays, and taps into a green wire by the battery junction box. I'm guessing that is the AC clutch wire.I have attached my tune file for viewing pleasure. But not sure if that will even help. I still feel like the fans kicking on and off could be a power problem possibly? Any help would appreciated. Thank you.

Is it possible the fan is kicking on when the ac compressor is kicking on? That it's tapped to that green wire. Do you have two wires going into your ecu? My aftermarket harness has 2 going into the ecu, one to the red power box on the driver side of the motor, and one ground.

My 2000 truck efans are set up like this. They operate properly.

https://photos.smugmug.com/Silverado..._190902-X2.jpg

https://photos.smugmug.com/Silverado..._190921-X2.jpg

I did suffer from low voltage at low idle with the AC on and both fans running until I swapped to the 145 amp alternator. Now that's no longer an issue.

Resolute,

That's exactly what is happening when I hit the AC button. But the fan, even if it's already running, cycles like it going in high then clicks back to normal. My AC compressor cycles on and off as well with the fans. My harness has 3 grounds, 2 power, one blue to the pcm, and one green to another green wire in a wire harness near the junction box

Shady,

Thank you for the screen shots. I will have to check mine out. I'm wondering if my harness isn't correct, or an older model. Maybe my AC needs charged up. Does your AC come on and work normal? At idle?

Sounds like a pcmofnc harness. Thats what i have, although i have a p59 ecu. Here is their 3 relay harness, tell me how close it is. I feel like maybe the green wire should go into the ecu as well, mine does anyways. Do you think that the fan is kicking into high because it is being fed voltage from the green wire? If you can post your tune up, we could maybe help you more. Also post up this "junction box" in your engine bay.

That sounds like my harness. My understanding when the compressor kicks on closed the relay sending power to the high speed side of fan 2. But only when the compressor is engaged. Doesn't seem right to me. I dont believe I can hook it to the pcm. Not sure if it has a high speed fan output. Also it would be looking for a ground. Not power. So the relay would have to be rewired. My tune is posted in the first message. I did disconnect the green wire from the ac clutch wire. It now doesn't surge on and off. Just no high speed when the AC is on. You'd think the green wore could just be hooked into the ac button on the dash with a relay. Sounds good in my head. I have to readjust my tune after fiddling with it be cause now my fans are always on and truck doesn't get any hotter than 180-185. I appreciate the help. I can snap pictures tomorrow.

This is what I mean about putting it into the ecu. Are you sure that green wire is a ground?

I tested the AC clutch wire for power. When it off it doesn't read anything. I turn my ac on with vcm scanner and I get 14v from the green wire. So I'm guessing it powers a relay to give fan 2 12v volts instead of 6. the thing is, is that it will only do this when the ac compressor kicks. Does your fan 2 go to hi speed when you engage the AC? When I control the fans with VCM scanner, the fan 2 option doesn't work. When i click fan 1 both turn on. I'm guessing the pcm doesn't support a high speed function? I would have to pull the harness apart to see where the green wire from the fan harness is actually supoise to go. Maybe to previous owner messed with it and it really is suposse to go to the pcm. I am running a P01 computer, original 2000 year

Just checked both fans. When I enable them I get 12 volts to each one. But they will not operate with one fan disconnected. Maybe I need an updated harness.