Another vote for getting your AC checked out. I also drive a 2014 Mazda5. If I turn the rear air on "high," the back cools down pretty quickly.... all the way back to the third row. Granted, our summers here only get up in the upper 90s, not over 100, but I've never noticed my AC functioning any differently than any other vehicle. My windows are tinted (factory tint), FWIW, and my Mazda5 is the dark gray color.