If you want to see it in action, park your Jeep and with the engine running, squeeze the sides of the glove compartment door until you can remove the door. Shine a light back at the cage - that's the air intake for the HVAC. When you have it set to fresh air, with it running, the cage door is closed to the inside, now turn the recirculate mode on and watch what happens. The door will lift and block outside air from entering, now it's pulling in air from behind the glove compartment.
Go back to fresh air again and wait for it to reset to the normal position and then turn off the engine. Now it will re-adjust again. It settles into a position where it's in between the fresh and recirculate settings. If you sit in your Jeep for a bit, you will also notice it will sometimes open, close, and re-settle again.