1999 Grand Prix, GTP, Sedan.  AC work and blows cold on the driver side but hot on the passenger side.  It has dual zone temp controls.  Driver side blows hot with heater on and so does passenger side. The controls seem to redirect the air flow fine.  I live in FL so I need AC, don't care much about the heater.  
I have taken apart the passenger side dash and don't see the hot/cold mixing box, thinking that the hot door is stuck open.  Any ideas or directions?