Oops. Sorry R J . I just saw that you had posted the same thing I did, except your's was 1st. I didn't see yours before because you had that part of your post under that diagram pic.
Sorry again.

 

The way it works; the heater core is always hot, the AC evaporator is on the cold side. Turn the selector to full red and the cold side is turned off, turn it full blue the hot side is off.
The mode switch choose which level. The recirc switch opens and closes the fresh air door (and turns the AC compressor on).

The left and right vents are separate from the center vents. Actually 4 different sets of ducts. Could something have fallen through the defrost vents?

Try the heat through the vents.

 

With the thought that , it’s very tight quarters in and under the dash board, it is unlikely that a piece of ducting popped off, or broke away.

Perhaps the temperature blend door actuator needs to be calibrated

https://www.chevyhhr.net/forums/www....ad.php?t=57384

read carefully and follow all the directions.

 

Heat works just fine. All vents were blowing hot air. What’s getting me is the two center vents being so different in temps. They’re right next to each other, so you’d think they’d have the same temps coming out.

 

Are those the instructions to replace the air temp actuator? It sounded like it calibrates itself.

 

Unless something got sucked into the distribution box.

 

hmmm.. I also turned my defrost vent on and I runs cold from passenger side to driver side. I ran my hand across it and the air got warmer as you moved to the driver side. Does that vent have one hose or is it split like the console vents?

 

Posted pix.

 

It looks like it’s just 1 vent with 1 hose.

 

Cold to Warm would direct me to the temperature blend door.