My C4 Picasso 10' have the same problem. There's not a hole within the A/C circuit and the clapet works properly. The A/C works but provide hot air on the drivers side (on the left). I focused that this hapens during hot days. A mechanical said that this car have one temperature sensor for each airflow output, so I will hack each output (especially the drivers with the screen) to check one by one the sensors.
Do any of you have informations about how to hack those outputs? I did a search at YouTube without results...