2005 Ford Excursion - A/C help HOT in Texas

My husband bought me a 2005 Excursion (V10) in December 2015 and at that time the A/C wasn't needed but now that it's summer time I'm sweating while driving around town. From what I've read it's because when the rear a/c is turned on the rear evacuator is working and sucking all the air to the rear. Is there ANYTHING that can be done to help?

The front and rear ac systems are connected. Seems to me that the ac system is low on refrigerant. That could cause the issue. If that is not the problem there is an issue with an orifice tube in the front ac evaporator or plugged up evaporator.