I had exactly the same problem on a dual zone system. Passenger side - like ice. Driver side, ambient. Mine is dual zone, and it made no difference if I selected Mono, or Dual mode, it was still always ambient on the drivers side.
I read a thread that said disconect the battery for 30mins, reconnect, leave for 10 mins, then turn ignition on. It's supposed to reset the position of the stepper motors which control all the flaps inside the system.
I did all this, and now.... well, I can't get any warm out of the system. At all. From any vents. Previously you could select AirCOn on, but set temp to Hi, and air would come out like a furnace - as it should. Now, setting to Hi never produces hot air. Aircon onaircon off, no hot air
I'll try it out properly over the next few days, then may try a battery disconnect again.
But if anyone else has this problem, please post your findings!