Have the same problem, heat on passenger side, cold air on drivers side. Have done the following the try to resolve issue:
Have replaced pollen filer, no joy. Via a breakers yard, have tried 3 air-con control units (no joy), and have disconnected the battery to reset all electronics, again no joy in fixing fault.
I did however notice about a week or two ago, that when starting the car, heard a creaking sound from inside the dashboard, like a ventilation flap trying to move. Am not hearing this noise anymore, and was wondering if something is jamming the flap or whether the motor controlling the flap is faulty?
If something is jamming it, is it possible to push something down one of the vents to clear it, or is this not recommended?
Your thoughts on the above would be very welcome as the weather is getting a bit cold at the moment