2007 Chevrolet Uplander AC Problem

Tiny
MIKEUPLANDER
  • MEMBER
  • 2007 CHEVROLET UPLANDER
  • V6
  • FWD
  • AUTOMATIC
  • 135,000 MILES
My Uplander's AC doesn't work, I can start the vehicle, the ac clutch comes on, the cooling fans turn on, the ac clutch turns off. No cold air comes out of the vents at all, I checked the pressures and have about 105 psi on the low side and about 365 on the high side.
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Saturday, July 25th, 2015 AT 7:05 PM

20 Replies

Tiny
WRENCHTECH
  • EXPERT
Sounds to me like you have done some self medicating and the system is severely overcharged. You can't just arbitrarily add refrigerant and expect colder air. You need to bring it to a professional and have the system completely evacuated, vacuumed and recharged with the exact weighed amount of charge. DO NOT try to use the system in the meantime as you will destroy the compressor if you haven't already.
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Sunday, July 26th, 2015 AT 4:30 AM
Tiny
MIKEUPLANDER
  • MEMBER
That could be the case, because I let my son borrow it for awhile, twice. He might've done that this second time, I'll see.

The first time he had it in the winter, he brought it back in the winter months, and I noticed the cooling fans would come on about 10 seconds after starting it. They would, and still do, the entire time you're driving the vehicle and don't shut off until you turn the key off. So it is exhibiting the same behavior, I'm just not sure of the ac clutch starting or ac pressures because you don't use ac in the winter. Could there be a switch problem somewhere that is the primary reason this all started? It also has rear ac, if that matters.
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Sunday, July 26th, 2015 AT 6:41 AM
Tiny
WRENCHTECH
  • EXPERT
You may think you don't use AC in the winder but that car is wired to engage the AC compressor whenever defrost is selected because it removes moisture from the air and you can't allow this to happen in it's present condition. I'm serious. If you ruin that compressor you are looking at around $1000 for a compressor, dryer and condenser to correct the damage.
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Sunday, July 26th, 2015 AT 6:46 AM
Tiny
MIKEUPLANDER
  • MEMBER
I'll call the Chevy dealer here tomorrow to have it checked out.

I'll make sure I post back on what they found.

I spoke to my son this morning he said he did add some, the last time he borrowed it, which was in the summer. He said he noticed the fans coming on like that in the winter but thought it was normal. With that being said, is there an underlying cause, that would make the fans come on and stay on like that even in the winter? The engine doesn't run hot, it hasn't been overheated, the coolant level is normal in the recovery tank.

Let's just say I go out, start the vehicle, leave the ac off, and all the rest of the blower, defrost, etc. Off. What would cause the fans to act like that.

Thank you for replying so quick too, I appreciate it.
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Sunday, July 26th, 2015 AT 8:12 AM
Tiny
WRENCHTECH
  • EXPERT
You would have to scan the computer for codes to get a hint of what is going on. There are many things that could cause that from stuck relays to a bad computer and everything in between to include someone that knows nothing about the system hot wiring it. I wouldn't rule that out in your case.
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Sunday, July 26th, 2015 AT 8:51 AM
Tiny
MIKEUPLANDER
  • MEMBER
Not sure how much trust to put into Autozone, but I just had them scan it about 10 minutes ago. There were no codes, it has no check engine lights, and I can assure you no one has done any wiring to the vehicle, except GM when it was new.
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Sunday, July 26th, 2015 AT 10:03 AM
Tiny
WRENCHTECH
  • EXPERT
This is a 2 speed circuit and pretty complex so you're probably going to need a professional to troubleshoot it.

https://www.2carpros.com/images/external/136855879.jpg.gif
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Sunday, July 26th, 2015 AT 10:08 AM
Tiny
MIKEUPLANDER
  • MEMBER
I understand the circuit, but I don't see the logic that tells the ECM to turn the fans on, other than the IPC telling it that the engine is hot.

Is there a sensor that is telling the IPC that the engine is hot located on the engine somewhere?

Looking closer at the engine, the fans actually turn on in slow first after approx. 6 seconds, than the fans go into high speed approx. 4 seconds later. I swapped the relays around making sure the ones I swapped were the same as the ones I was swapping to. They all showed the same symptoms, so I'm pretty sure its not a relay problem for the fans. I unplugged the ac relay and the clutch doesn't engage at all, like it was previously, but it still followed the process it was before.
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Sunday, July 26th, 2015 AT 12:12 PM
Tiny
WRENCHTECH
  • EXPERT
There is an electronic coolant sensor that the PCM monitors for many functions to include fuel mixture and numerous other components. If you have a scan tool you can look at the reported coolant temps. The fans are not only regulated by temperature. The PCM monitors AC pressure also so you could even have a shorted out pressure sensor. That could also be seen with a scan tool.
That diagram only shows the circuit that operates the fans, not the logic that operates them. The PCM controls the relay trigger ground to turn them off and on.
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Sunday, July 26th, 2015 AT 12:19 PM
Tiny
MIKEUPLANDER
  • MEMBER
Do you know the location of the ac pressure switch on this vehicle so I could do a visual of it.
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Sunday, July 26th, 2015 AT 12:47 PM
Tiny
MIKEUPLANDER
  • MEMBER
Or the ac pressure sensor?
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Sunday, July 26th, 2015 AT 12:48 PM
Tiny
WRENCHTECH
  • EXPERT
https://www.2carpros.com/images/external/120410838.jpg.gif
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Sunday, July 26th, 2015 AT 12:49 PM
Tiny
MIKEUPLANDER
  • MEMBER
Is the PCM looking for a normally open or normally closed from this switch?

So I could unplug it and see if the fans act normal?
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Sunday, July 26th, 2015 AT 2:19 PM
Tiny
WRENCHTECH
  • EXPERT
Neither, That is not an open/close switch. It's a 3 wire, 5v reference that delivers a specific return voltage that translates to a specific pressure.
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Sunday, July 26th, 2015 AT 2:22 PM
Tiny
MIKEUPLANDER
  • MEMBER
Surely its designed to turn off the fans if the switch opens?
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Sunday, July 26th, 2015 AT 2:33 PM
Tiny
MIKEUPLANDER
  • MEMBER
I don't think that image is for my vehicle, my oil filter is on the backside of my engine and I didn't see a connector on the ac line back there.
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Monday, July 27th, 2015 AT 5:31 AM
Tiny
WRENCHTECH
  • EXPERT
Not surprising. You still haven't told us what engine you have so I had to guess.
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Monday, July 27th, 2015 AT 7:35 AM
Tiny
MIKEUPLANDER
  • MEMBER
It's a 3.9L V6 non flex fuel, it looked like that pressure switch for the high side is down by the compressor between the radiator and engine.
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Monday, July 27th, 2015 AT 11:31 AM
Tiny
WRENCHTECH
  • EXPERT
The diagram I gave you was supposed to be for a 3.9
The switch is easy enough to find if you just follow the high pressure line.
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Monday, July 27th, 2015 AT 1:45 PM
Tiny
MIKEUPLANDER
  • MEMBER
Problem was fixed, high pressure switch was bad, switch location is between the radiator and front of the engine. It's about 6-8 inches from the AC compressor.
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Monday, August 3rd, 2015 AT 4:55 PM

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