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HVAC Controls Freezing - Dash Temp Reads "---"

HVAC Controls Freezing - Dash Temp Reads "---"

Postby smashZ71 [OP] » Mar 22 2016, 8:46pm

Hey folks,

Does anyone have any experience with their HVAC freezing up? Was the cause the HVAC module going, or is something causing it to freeze up, like a bad outdoor air temp sensor, or a bad resistor pack?

Here's the back story:

I've got a 2012 GMC Sierra SLE with the basic HVAC system. Three knobs, 2 buttons + A/C.

For the past few months my outside air temp on my dash board randomly reads "---". It used to be once a week, now it's once a day. Sometimes right away, sometimes after 2 minutes of driving. When this happens the A/C doesn't work because it's locked out because it has no outside temp.

More recently the HVAC controls have randomly stopped working. The lights don't come on, and the buttons / knobs do nothing. This only happens when the dash reads "---", but not every time; about once every 3 days.

For both cases above, turning off the truck and starting it back up again will resolve the issue. Sometimes for the duration of the drive, sometimes only for a short while.

I pulled a code, which off the top of my head I can't remember.. but it was a "U" code, and the translation was unable to communicate with the HVAC module.

Does anyone have an idea of where to start with this? I'm not even sure how the outdoor air temp ties into the computers. (Directly to BCM, Dash, or HVAC module)

Thanks in advance,



Kevin
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The dashboard with ---
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Re: HVAC Controls Freezing - Dash Temp Reads "---"

Postby esox07 » Mar 23 2016, 11:11pm

Will your HVAC controls work if you put it into Manual Mode? If you want the A/C you can just turn the temp all the way down to its minimum and then adjust the amount of cooling with the fan speed, kind of like it used to before all the AUTO stuff. Same for heat, turn the temp to max and then use the fan controls to determine how much heat it puts out. By setting the temp to its max, you lock the heat on and by setting the temp on the Climate controls to its min, you lock the A/C on.
I realize this doesnt solve your problem, but it might allow a work around until you get the root problem fixed.
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Re: HVAC Controls Freezing - Dash Temp Reads "---"

Postby GMT604 » Mar 24 2016, 1:45am

Ambient temp sensor is connected to the HVAC panel, which reports it to the cluster. I would suspect a bad AC panel, specially with the no communication code. Unless there are other no comm codes as well.
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Re: HVAC Controls Freezing - Dash Temp Reads "---"

Postby smashZ71 [OP] » Mar 24 2016, 4:27pm

That was the only code present.

The only other thing that **may be relevant is that I swapped out the stock stereo for an Android touchscreen unit from china. ( < $400 delivered, how could you not! ). I bought all the proper harnesses and pigtails so I didn't have to cut into the factory wiring. I'll pull it all apart first just to make sure I didn't kink an HVAC wire somewhere, or miss getting a connector in properly. Honestly the problems started almost a year after the upgrade so it's doubtful.

I'll keep you posted. Thanks for the reply,



Kevin
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Re: HVAC Controls Freezing - Dash Temp Reads "---"

Postby smashZ71 [OP] » Mar 24 2016, 4:30pm

esox07 wrote:Will your HVAC controls work if you put it into Manual Mode?


When the lights on the knobs don't light up, I get nothin. Turning the fan full on or off is just off. I can't hear the blend motor's going either. It just dies.
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