Hatzie
 

You are very knowledgeable about these hvac systems and their quirks. I have a couple of questions for you.
My 2003 Tahoe has 264,000 miles on it with dual climate controls, digital display.
I disconnect the battery between uses as we don't drive it often.
I have trouble getting heat right now. The radiator is good, heater core has been flushed, coolant level full, hoses hot to the heater core.
I found the only way to get good heat is to run the temp all the way up to 90* and to get good AC run the temp all the way down to 60*. At any other setting the temp wanders. It can turn from hot to cool in 2 minutes time on either heat or AC on it's own. As I adjust the temp the numbers are all over the place. I read where one guy pulled the temp knob and sprayed mass air flow cleaner in there to clean the potentiometer and it worked for his display. ?
I know the blend door actuator moves by input from the control panel so is my control panel bad? I see the usual recommendation is to do the reprogram. And why does an hvac system need to be reprogrammed so often? Thanks

Re: Hatzie
 

There are seven sensors that affect the digital HVAC control system.

1. The interior temp sensor with a fan with a cover that looks like a microphone or tiny speaker grille in the headliner above the drivers' head. GM calls it an Aspirator. ACDelco GM PN is 22834330
2. The Ambient outdoor temp sensor in the framework under the RH turn signal lamp. ACDelco 25775833
3. Four Instrument Panel Air Duct Air Temperature Sensors.

   1 Upper Left, 2 Lower Left, 3 Upper Right, and 4 Lower Right.

4. Sun load sensor in the centre defrost grille in the dash. Usually affects the AC.

Look at the outputs from these seven sensors with your scan tool.
My gut tells me the tiny aspirator fan has failed as that is a common issue.
That sensor assembly is not super cheap. At $30-$40 I would check it first. I wouldn't just load it in the parts cannon and say your Hail Mary.

The other thing that could affect your Heat is an air bubble in the heater core. It's common for my W-Body Impala but I haven't had that issue with my truck.
Park the truck on a fair incline and run the engine at 2,500 RPM while filling the coolant tank to the MAX mark with Dexcool.
Park it on the level and draw off any excess til the coolant is just under the max line at operating temp.
Your other option is to use a vacuum cooling system filler tool.

Re: Hatzie
 

Good Lord. This system is more complicated than I imagined. That aspirator, I have wondered what that was over head. Thank you for the info.