Almost 5 years later and I am having the same/similar issue:when I am driving the right side defrost vent is blowing cold. I would think it is heat flap servo, but where is it at. is this a common problem?
Thank you so much for the reply.I probably won't see the OP reply, since I was looking for another problem for my CC. I read your problem and decided to register to give you an answer.. your problem has to do with the temperature sensor. Since is a Dual Climate Zone, there's a temperature sensor on the left and right side of the vent. That sensor comunicates with the ECU. Whenever the sensor goes bad, it sends wrong information (temperature readings) to ECU.
I.E., you have the heater blasting on both sides, right?
Now, the drivers side blows hot (80F), but the passengers side blows cold. Driver's side vent sensor reads 80F so there's no problem there.
Passenger's side however, when sensor goes bad, it reads somewhere around 160F. The ECU "sees" this, and its trying to "compensate" by turning the heat lower on the passenger side.
Long story short, remove the side cap/cover on passenger side, you'll see the sensor on the duct installed upwards. Remove it, replace it with one from junkyard or a new one. Your problem will be solved!