I have the dual air controls. My dealer fixed this problem for me by totally draining the system and refilling to full specification. Apparently, they use a mixture that includes some oil and they believe the oil settles and somehow precludes cooling on one side. I thought it sounded as logical as the cow jumping over the moon - but, that is their story and they are sticking to it.
Anyway, this was done at the direction of DC's area warranty representative. They did this last year and it worked until the winter. They did it again 3 weeks ago -- So far, the passenger side is about 2 degrees warmer than the driver's side. I do not know if this will become an annual service item or if it is a true fix, but I'm suspicious that it will be an annual service requirement.