2007 Silverado classic Cooling fan running

Dennis Ellert · February 6, 2020

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

carnau · February 6, 2020

3 minutes ago, Dennis Ellert said:

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

Are you sure there are no codes in the vehicle or is the light just not on? The reason I ask is because a p0128 can set in the ECM and not turn the engine light on. Does the coolant temperature gauge on your dash work? If the thermostat is the wrong degree or it is stuck open it will not allow the truck to get to operating temperature and you will get this code and this will cause your vehicle to run the fans at full speed. A cheap code reader will also not tell you if the 128 is there because it isn't setting as a A dtc but a B catagory DTC since the truck is not overheating.

Dennis Ellert · February 6, 2020

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

rjgti · February 6, 2020

high pressure switch will send a signal to ecm/bcm to command fans to high. it is your most likely is your issue

tlaw91 · February 6, 2020

So did or did you not replace the pressure sensor?

-GM Tech

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Burnham Mikkey · February 6, 2020

Do any of yal k ow anything about unlocking my stereo in my 2000 silverado the 800 number is not working

Dennis Ellert · February 6, 2020

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

tlaw91 · February 6, 2020

I’d be checking into a partially restricted a/c system.

If you plug in the sensor and the fans turn on the ecm is seeing high pressure and is trying to lower it using the cooling fans

Maybe the desiccant bag is coming apart or you have a compressor coming apart or another common one is someone over oiled the system and it’s collecting in that area tricking the system into having a build up of pressure in that area.

That’s the direction I would be heading.

Hope this helps

-GM Tech

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Dennis Ellert · February 7, 2020

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

tlaw91 · February 7, 2020

Hope this helps

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Dennis Ellert · February 7, 2020

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

davester · February 7, 2020

you may be able to find a pdf for the wiring diagram for your truck on gmupfitter.com, or, failing that, a subscription to the full service manual at a site like alldatadiy.com. It'll also have the diagnostic procedures to figure out where the problem is. I highly recommend it, particularly if you work on the truck yourself.

tlaw91 · February 8, 2020

PM me your email I’ll send it that way! We’ll get it to you somehow to fix your truck!

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carnau · February 8, 2020

On 2/5/2020 at 8:50 PM, Dennis Ellert said:

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

Right. I understand it is not overheating. It is probably running to cold to be honest. Is the coolant temperature on the dash reading normal? If you have a p0128 DTC it will do an engine hot ac off fault. If the AC has a fault ( the low pressure sensor disconnected ) it will only look for the overheating concern and not turn your fans on high because the AC system is not able to run and the engine is not hot. And it may not even be a code.

If you have a Snapon scanner go to the data for the engine. Go to your special functions and fan speeds. Plug the switch back in and see if it shows fan speed 3 (that should be all of your fans) enabled. If it does show enabled then the system is trying to work as designed and we need to find whats causing it to turn the fans on. If it is not enabled let me know and we will go a different route.

You're overlooking something and unplugging the switch is just causing a different problem not allowing the real problem to be fixed. By that I mean if for instance you have a noise in the vehicle while driving, if you take the starter off the car, you will no longer have the noise because the car will not crank and drive. Your noise is gone but now you have a different problem, So disconnecting the switch means your fans are not running, but you have a different problem. (no ac)

You are right though, throwing parts at a car is not going to solve this issue. Lets diagnose the vehicle and find out what the real problem is.

If your scanner is really nice it will also give you the reason your fans are enabled.

carnau · February 8, 2020

Something else I just thought about. If your ac system was overcharged or the high pressure sensor was reading high it could cause the fans to run on high because it would be trying to cool the condenser in turn bringing your high pressure down.

If you have an AC pressure gauge set, plug it in and see what your high and low pressure are. If your pressure is high (over charged system, restriction in the system) this could be the cause.

He is the schematic for the system.