Blowing cold air on passenger side when heater is on; I know could be Dual climate valve or servo doors…anyway to tell what is most common
You have both sides set to the same temperature and then set it to automatic and single temp control? I’ve seen some automatic systems get confused.
If you hear a faint click click click… it is the blend door
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With these automatic systems (which I hate - just give me some old-fashioned cables or even vacuum lines), it’s nearly impossible to deal with issues without error codes. The error codes will more than likely be body codes (Bxxxx), and not be read by generic code scanners (such as those used at big-box auto parts stores). You’ll need to bite the bullet to pay a shop to read the codes, or buy a scanner that is powerful enough to pull things beyond generic OBD2 codes. If you want to go the latter route, I can make a suggestion but you should start by just searching around the web.
Electronics are much more reliable, like it or not. I’ve heard stories of Mercedes Benz vacuum line actuated systems being a bear to keep up with.
I’m talking about the ease of fixing things when they break. And in 40 years on the road, the only system I’ve had trouble with was electronically controlled. And the issues had to do with diagnosing exactly what needed to be fixed.
The driver side vents go from hot/cold when you adjust temps?
A desktop computer has billions of electronic (transistor) switches, and one on/off switch. Both are electronic switches; but it seems pretty obvious which type of switch is the most reliable. Better reliability factor applies to electronics that have no moving parts, but not nearly as much for electro-mechanical actuators. I’ve been driving for 55+ years, and never had a single heater door failure. All have been non-electronic cable actuated designs.
I’ve been a licensed driver for 38 years. If I’m counting correctly, on my personal cars I’ve had one electric actuator failure, two vacuum servo failures, and three cable or lever failures.
So you have no experience with electronic blend door designs. Kind of hard to draw conclusions on their reliability.
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Presumably in this discussion “reliability” means how likely something is to break? That’s not the issue here. Something in the OP’s system is broken. So F* “reliabilty” - that’s out the window. The damned system is broken - not “reliable.” So then the issue became once something does actually break (which it apparently has in the case of the OP) how do you figure it out? That’s where - among SOME people - without fancy diag devices - one might wish for the older simpler systems of things like cables and vacuum controls where finding existing problems is more straightforward. You’re crawling down under the dash in either case.
Questions of “reliability” don’t apply here. The OP’s systems is BROKEN - UNRELIABLE.
My own preference for simpler systems does not solve the OP’s problem, to be sure. I just made yet another off-hand comment that I prefer systems that are easier to diagnose ONCE THEY’RE BROKEN. And then it suddenly became something like “oh, but this new more complicated sh** that are computer controlled and for which computers are required for diagnosis are better…” You know what? In some ways and by some criteria, sure. But in others, not so much. We’re already too close to needing a manufacturer specific scantool to know what our damned tire pressure is. (TPMS warning light? Take the car to your dealer service department. Cha ching. That’ll be $100 to check your tire pressures with our special proprietary scantool… "Oh, but gee. That’s so much “safer” and more “reliable” Ooooh Ooooh.)
The moment that manufacturers give me access to their proprietary computer diagnostic software at the moment that I own one of their cars (new or used) is a moment that my attitude will change - at least a little. But I’ll still ask for simpler over more complex.
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quote=“cigroller, post:5, topic:194197”]
With these automatic systems (which I hate - just give me some old-fashioned cables or even vacuum lines
[/quote]
Seriously . . . ?!
It’s no easier to replace vacuum actuators and hoses under a dashboard, imo
And some of the actuators are INSIDE the plenums 
I’m talking about diagnosis.
Okay
But I still don’t think HVAC systems with vacuum actuators are any easier to diagnose
You can check vacuum with very accessible and very cheap devices. Not so with the electronic systems.
So to be clear, a bit of what I’m saying is coming out of some headaches I’ve had with my '02 Envoy’s auto HVAC system. First, I think if you polled owners of such things you’d get pretty high levels of complaints about lack of reliability. (The cheap plastic gears inside of the actuators like to break - which can happen to any of them, but GMs seem to be “special” in this regard). Second, once the system isn’t working correctly, unless you’re just going to throw parts at it, then you need to be able to read body codes (back to my first point in this thread), and if you really want to effectively deal with it on a GM, then you need a Tech 2 scanner. A basic vacuum gauge is easily available in many places for $20 or less. You find me a Tech 2 for that and I’ll kiss your feet.
Well, we’ll just have to agree to disagree 
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I much prefer a cable to a vacuum actuator design for the heater. The vacuum method complicates diagnosing engine problems involving the intake manifold vacuum system. If the vacuum source was a separate a vacuum pump, maybe ok. I guess I’m lucky w/cable actuation, the only car-related cable failure I’ve experienced is the clutch cable linking the pedal and the fork on my VW Rabbit. Easy fix.