AC only blowing cold through driver's side vent.

[oldskoolaudi]

Long story short, I have a 2004 X5 4.4i and the ac was not blowing cold at all. Talked to my dad's indy friend and he said normal operating pressure for the ac system is 25-30 psi. My dad put his guages on it and it read 25 and so we put a little more 134 in to get it to 30 and the ac worked much better for the next week. But as of a week later, the ac is only blowing cold through the drivers side vents and not the rear or passenger side vent.
I've been reading posts that say it's an improper charge but how can it be blowing fine on one side and not the other. Is there some type of door or valve that's suppose to be opening or closing that's not working properly. Thanks!