Aircon Blowing hot on passenger and cold on driver side

[Kev h]

Hi, only purchased my A6 Sline recently. I have noticed that the drivers side air con wont heat up even when ran on HI for a bit. The passenger side will blast out hot air but driver is stuck on cold air. After some reading on different forums I think that it might be the flap motor stuck in a position so the air the air isn't mixing. 

1. Does the flap motor sound like the culprit and if so wher are these motors located.

2. Are they easy to replace, and would someone know where to get them for cheapish.

 

Thanks