"Dual" dual-zone air con...

[Roadhouse]

Hey all.

Got my 2004 4.8is with the dual zone a/c. Pretty straightforward - set the temp to the desired degrees and away we go. Or so I thought...

Question is, what is the point of setting the temps to the desired figure (say 22 degs C) if the scrolling knob between the vents towards the centre-top of the dashboard allows you to pump in hot or cold air? Perhaps it's a convenience feature so upper body air temp is controlled by the knob. Not very convenient as I have to keep adjusting it...

If I just wanted to control my a/c via selecting an actual temp, what position should the scrollable knob be in??

Has me a bit baffled - what do others do?