I am not experienced with posting. But I recently went through a lot trying to fix my climate controls on my 2013 suberban ltz 4x4. And I have a few observations and what I ended up finding as a solution that was unexpected.
1 there's at least a dozen different descriptions of how to reset the climate control computer very slight differences and I must say going through all of them you lose track of what worked and what didn't. Would be nice if there was a set approved method to rely on.
2 there are many ppl looking for answers and many posts telling them which part it might be, but very few that start off saying "have you had battery issues recently?" Because if you have it can make everything out of sinc and malfunction. Getting the system to re sinc instead of buying parts needs to be a better known possible solution to try before investing in parts.
3 my solution ended up being the main actuator that controls the main vents had lost it's tightness and one of it's screws. No solution I found worked because it was a very simple one. Not a usual issue to be sure but in this world of easy fixes and buy a new one solutions I think we all forget sometimes to check the very basics before we dive into the deep end looking for the complicated. That one piece not being attached correctly made the main vents blow only cold. No fan position change possible. Rear heat worked but the combination was a bad thing. A windshield that was constantly fogged and that can be dangerous trust me.
I am not expert, I know enough to get me in trouble. But I thought some posted hind sight might help someone else pulling thier hair out looking for answers. I ended up taking my entire dash apart and checking each piece one by one to verify operation. And finally saw the issue. All I can say is I am very glad I didn't buy a 250 dollar head unit like many parts stores suggested. With no heat and no fan position control the usual answer was the head unit. Thankfully all it really required was time and effort. But a post like this might have saved me some time. And that is the goal behind creating this one.
Thanks for reading.

 

Good work, M0rt1s! The part stores are there to sell parts, although they will often install things like batteries. Wish I'd had have them install my new AMG battery a few months ago. That was one large and heavy AGM battery, along with the old one.