I'm having the same problem the OP is having, A/C blowing out of the top an floor.But what's strange with my situation after you drive the car an hour or so, it will open up and start blowing cold air out of the vents.Is there another vacuum check valve located somewhere else besides what was mentioned in thread.
The "blend" door will stick in that position, especially if it hasn't been used for a while. Manually operating it (gently) can restore the functions, if there are no other issues.
Hth.
Anything other than stock is unappealing to me. But I like heat defrost and ac to work in my cars.
After market setup with cables instead of vacuum can work but massive pain to install I would think.
The stock HVAC box is clunky and some folks remove it all together for easier access to that side of the engine.