HVAC operation

I'd track the cable and see if something is binding it or in the way of the control arm at the end.  And pulling the glove box liner might give you a better view.  But, my guess is that the hinge isn't working.

You can see the diagram of it on Page 84 here: http://www.garysgaragemahal.com/heating-ventilation--air-conditioning.html.

If the cable wants to work and the door is the problem then we will need to point you at the right instructions for that, but one thing at a time.

broboyle wrote

...it gets stuck when moving the temperature from cold to warm (left to right). The lever gets stuck in the middle (shown in green in the attached photo). ... How can I troubleshoot this issue and what is the fix?

Probably just zip-tying the aftermarket radio wiring out of the way would fix it.

But you have to see what the interference is, to be sure.  Pull the radio, and if the lever still catches, try to disconnect the cable from the door lever on the firewall.  If it still catches: either cable is binding, or there's something inside the lever mechanism.  If not, it's probably something that fell through the defrost ducts, and is binding the temperature blend door.  It's relatively easy to pull the glove box & heater core to look inside the duct at the door.  Click each of these & read the captions:

I am thinking it is the aftermarket radio harness. I just got a new radio about a month ago and I am assuming the harness dropped down and is interfering. I will pull the dash bezel and see what is going on back there and report back! Thank you!

If you find the cable needs lubing it is not hard but you need to remove the cable.

Tools: cable, baggie, rubber band and lube of choice.

Poke the cable thru a corner of the baggie about a 6" to 12" and pull it back up to the end of the outer part of the cable.
Wrap the rubber band around the baggie holding it tight to the cable.
Now slide it baggie & rubber band up to the very end of the outer cable.

Find a place you can hang the cable from the baggie end for this next part.
Pour a little of the lube of choice in the baggie, it does not take a lot.
Let the lube work it's way down the inside of the cable.
Maybe move the inner cable in and out a few times to work the lube.

Also note when the lube makes it's way down it will drip out so have something to catch the drops.
Dave ----