George B
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I only have one of those little grills above the driver seat. None anywhere else.
What did you do to your NNBS GMT900 Tahoe/Yukon Today?
- Thread starter phattyford
- Start date
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the only other possible location I know of where there could be another one is in the headliner is drivers side rear way in back by the hatch, nothing there?
George B
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Nope, only have one sensor above my head.
George B
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Nope, only have one sensor above my head.
George B
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Now this is back on my mind. I don’t know why my HVAC acts this way.
weird, then the calibration on mine would do you no good because mine has 2 sensors, my initial issue was it was looking for a 3rd but there isn't one.
you might want to take the rear hvac panel off and use the tech2 and observe it as you adjust the temp, I see you noted the commands being in reverse it seemed like that to me as well when I was testing mine I think that is normal.
if nothing else you could just install the most current calibration and see if that fixes it.
George B
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I just went on AC Delco TIS and looked up the calibrations and they are all current. I should have taken a screen shot of the sensor readings at ambient before I started the truck today. I believe one of the rear sensors was reading 77* when all the rest of the sensors were reading 73*. Not sure if that would be enough to cause it to not act right.
there is one of the little sensors in the back vent tube either right where it splits up/down or right after I don't remember, I just know I bought one because I thought it was the problem on mine because I couldn't find the 3rd one it was saying it was looking for. I took it out and confirmed it had 5volts at the harness and then tested it by blowing warm air across it while checking the ohm's and it tested good. it's kind of hidden because they are black and small but they are there apparently there several in all these trucks front and rear about 6 or 7 of them. I think a new one was about $20 or so, if yours is giving a funky reading I would just swap it out and see what happens
George B
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I let it settle a bit and all the ambient sensors seem correct. I also compared the duct readings to a good thermometer and found them accurate.
What I notice about the temp and mode doors is that they all seem to work correctly when I am adjusting modes and temperatures across the full range. Both the front and rear follow as expected for both temp and mode. It's in auto that I see the challenge. when in auto max AC and max heat follow as expected and the mode door counts are the same as in manual but it's when it tries to mix in between that I get an issue. say I set it for 75* and it's winter so it should want to heat, the front will heat and blow to the floor while the rear will stay in split mode and not move it's temp door to a warm setting so it blows cold out the upper vents.
For now the fix is to just tell the kids to close the upper vents and use the rear control to adjust but I think it should work better that that.
George B
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One thing I don’t know is how the rear controller plays a part. It has a different calibration in it than what TIS says it should have. This is a pre-programmed one I got from rock auto.
