(Solved) Mercedes aircon blowing hot on driver side, thermotronic 4 zone

Problem:
I have now had two duovalves replaced under warranty, the second as the first was replaced under warranty and now the warranty has expired, but now the dealer says the Actuator motor is faulty and needs replacing, how does this affect the airflow, where is it located and is £1300 for the part and 8 hours labour reasonable. What would a good Indy charge for this to be replaced?

So after agreeing to goodwill at 51% and booking the car in, the dealers have had it for 5 days and still can't fix the drivers side blowing hot and the rest of the car cold. It wasn't the stepper motor or the control unit behind the dash, they are currently looking at the heater box, but can't find any messages in STAR DIAGNOSIS.

Solved:
Finally all resolved, was the stepper motor, as they had previously thought, but had to use trial and error to find the right one. So after 7 days it's all working as it should. Just goes to show that good old fashioned logic can work if your ignore the diagnostic software and go with your gut. Having some help from the forum and having a little understand from the WIS, helped me point the dealer to keep trying the motors. Final price was £650, as I got 51% goodwill and also a further 6% discount.

The use of a 2015 facelift c250 premium plus estate for the 7 days was nice too!