In my 05 GMC, sometimes the driver side vents will get stuck blowing fully hot or fully cold. Passenger side always works as normal, just the driver side has this issue. It's a dual climate control system. I've read threads on this before and I usually turn it off and turn the key in a certain way that resets it (for a while). I think it's about time to fix the issue, but is the root cause most likely one of the blend door actuators at the bottom of the dash or the controller itself? If it's an actuator, which one do I need to change out first?

 

The driver side blend door actuator....

 

But where is it located specifically?

 

Is your truck equipped with bench or buckets? Either way there is a cover that bolts to the bottom of the hvac housing, once you drop that the driver blend door actuator should be on the side of the box, and accessible fairly easily

 

Pull the hvac fuses and force it to relearn... Key cycling does absolutely nothing. I have had to do it 4 times at once to get my 05 to smarten up but it does. Haven't done a blend door motor yet at 175000 miles and only usually have issues when I disconnect the battery lol.

 

My 05 Z71 RCSB was doing the same thing, just the driver's side vents blowing hot. I bought AC Delco part 15-72971. The blend actuator for the driver's vents are actually on the passenger's side, just above where the passenger's left foot would rest. It's about a 20 minute job.