My 2002 1.9 TDI Avant has developed an interesting aircon problem.

Regardless of the temperature set or whether ECON is on or off, the flaps are constantly moving in a seemingly random manner. Most noticeable when trying to demist the screen because the air gets directed that way, then into the cabin, then back again - all very random.

In terms of reaching the required temp, it does get there in the end but i notice the direction and temp of the air changing throughout any journey. Can't be right?

Any thoughts? Does the control unit sound like the problem? If so, how much are these?