I believe you have an electronically controled dual zone climate control in the front. If the passenger side actuator is faulty, this might explain your symptoms.
Unfortunately, this actuator is not easily serviced. My repair information suggests that the passenger airbag, dash, and 1 vacuum actuator need to be moved in order to access this temperature control component. It seems to be located just in front of the console. Removing the glove box may be helpful.
Diagnosing a faulty temperature actuator include: 1) A/C will work for 1-2 minutes when engine is cold. 2) If you can "pinch off" the heater hoses going to the front heater, the A/C begins to recover. 3) Sometimes an audible clicking noise can heard.