Dennis Ellert

Thank you for the reply. I think you are right, I"ll plug the pressure switch back in and start over again, however I am not sure if my scanner can provide the info needed and I'm not sure I am a good enough scanner user to get the info I need . Also I am leaving for a ski trip to Montana next week and wont get back to that truck until the week after that. I will revisit this site and report what I learn after I get a chance to work on the truck again, but probably won;t be until close to the end of the month. I very much want to thank you for your ongoing help, you have steered me in a different direction. I will report what I learn. Thanks again Dennis.

Sorry but the short reply is no. That wiring diagram appears on my computer just slightly larger than a postage stamp. When I print to paper as large as I can it is 5" across and blurry. These old eyes cant read any of the print. I do want to thank you for replying so quickly and trying to help. Dennis

Ok ,, I read your reply...Think about this-- Truck has not had AC run for 2 days...if I start the truck when it is cold with AC turned off the compressor will not run AC.. and AC gauge set says high and low side resting at 70#...the cooling fans will still run on high after about 10 seconds of starting the truck... if I unplug the 3 pin pressure switch above the compressor the fans will turn off. if I plug the 3 pin connector into the old switch (the one I replaced) The fans will start to run even when the engine is cold,,, the temp gauge says cold,,,the AC switch is off,,, the compressor is not running,,,my thinking is the problem must have something to do with that pressure switch, the wiring to it, or the ecm. Now the switch and the ecm have both been replaced with no cure no change, So i'm leaning toward wiring harness,, But I don't have access to a wiring diagram, and sometimes a person tries to diagnose a problem and thinks he has it narrowed down and so he keeps looking the wrong area,, sorta like when you look for your lost keys or glasses and after a long time you break down and ask for your wife's help and she finds them in plain sight in a place you could swear you looked straight at. I'm lost on this one, maybe I;m missing something simple, you know,,, like maybe i'm making an assumption subconsciously. Possibly someone else has seen this before ,or maybe if someone reads carefully everything I wrote they will pick up a mistake I made. A wiring diagram MAY help. I have worked on this so long that i'm starting to doubt everything I THINK I know. Frustrated as hell. Dennis

The AC pressure switch was replaced ,without any change in operation,,,There is a possibility (slim chance) that I got a new defective switch. That part was over $70.00 and I don't think it is wise to buy another without doing some Real diagnostics. If a truck owners method of repair is to throw parts at it until it works I'll need deeper pockets and a lot more patience. Thank you for your quick reply. Dennis

Hello, thanks for the reply. The truck is not overheating. If the fans were running because of a fault in the cooling system, then unplugging the AC pressure switch wouldn't stop the fans. IN fact they will turn on and off as they should if you just let it idle with the AC pressure switch unplugged. I have run this truck ever since fall with the switch unplugged and it works fine ,,It gets warm, the heater works, and it dose NOT overheat. My scanner is a Snap on that cost me $2400.00,, It better catch all the codes. I am convinced the fault is somewhere in the AC system,, or wiring harness, ,A wiring diagram of that pressure switch and related 3 prong plug and harness may help. I would like to know what is normal voltage (or ground) at the 3 pins of the switch above the compressor. Thanks for any Ideas or experience you have on this problem. Dennis

I have a 2007 Silverado Classic that has the 4.3l v6. Last summer I noticed that the cooling fans were running on High whenever the key was on even when the engine was COLD. Here is what I have learned so far... the fault lies in the AC system....Coolant relays are new... ECM is new...and coolant switch is new...If you start the engine the coolant, or cooling fans will come on high after about 3 to 10 seconds. If you unplug the pressure switch (22878731 changed up to 13587668) the truck works great and the fans will only come on if the engine gets hot...BUT the AC will not come on...truck interior gets hot.. If you plug that switch back in the ac will work but cooling fans will run on high even when the AC is turned off...This is accompanied with an annoying higher idle that is not noticeable if the AC is running... Their are no trouble codes and the truck works great all winter with the sensor unplugged because I don't need AC in the winter, but I need it fixed before spring. Anybody see this problem or know what to do about it?? Thanks Dennis