I have a 6th Gen '05 and the last couple weeks I've had some weird issues with the HVAC, the blower will randomly change speeds, the air randomly changes from foot well, to torso to defroster, all these regardless of where the ***** are set.

Am I right in thinking that this is an issue with the actual HVAC controls in the dash?

The Resistor module and blower are both about 2 years old.

 

I have a 2000 Monte SS. The AC started blowing out the different vents without changing the selector ****. The selector vent has a vacuum controlled diaphram pulling against a strong spring. If the HVAC vacuum line loses vacuum anywhere in the system, the vent defaults to defrost as a safety measure. I traced my vacuum lines from the top of my engine, across the cowl just below the wipers, down under the battery area. As i faced my Monte, I saw a small bracket holding the vacuum line. The line was completely broken in half. Using some rubber washer line, I repaired the gap. My AC returned with full functions. I hope this helps.