On my 2010 Panamera S, my rear passengers don't seem to get strong AC coming from the vents like the front has. I don't have the 4 way temp control. I notice that within the PCM there are different AC controls (auto circulate, vent cooler etc...) but after playing with the various settings I don't seem to notice a difference. Any advise?

TIA...

 

From my Cayenne maintenance experience, I would check a couple things.
If you turn off front zones and only use rear zones, do you hear the blower pumping air? you should hear the back side blower working.
If you hear it but not much air is coming in, it is likely that the servo motors responsible for changing volume of air into cabin through rear zones, are getting old.
On cayenne there are some servos near the control module in rear console. There are some on the rear blower housing itself too. On Cayenne rear blower is a hassle to get to, but do not know on Panamera.
My first guess is, assuming your AC is not leaking, servos are failing and need replacement.

If you have durametric, there are tests where you can try to move servos, and if you are not getting the proper range, that is the reason - old servos.