My wife's A6 has got a strange climate control problem that I've tried to characterise and have performed the climate diagnostics from the http://www.audiworld.com/tech/ pages (It says its for A4 but i get some results but not those listed).

The symptoms are:
1. The ambient temperature display is often missing and its disapearance seems to be linked to selecting settings on the climate control
2. The air con clutch works - it can be heard when selecting between economy and normal. But when not in economy there is a constant chattering from where (i believe) the fan relay is under the dash, but this doesn't appear to impact the engine load. With one side set to 'LO' cold air comes out so i assume teh aircon is working ok even with the relay chattering.
3. When first switched on the climate control often goes into windscreeen demist mode for appox a minute then will change to another mode (not always the same). Sometimes after the minute or so the system will just go to idle, low fan speed.
4. When climate control is switched off I can still hear flap motors adjusting (presumably trying to get to a default position?)

The car is a 1998 A6 Avant. I performed the climate control diagnostics as shown in audiworld. I had the ignition on, and switched the climate control on to economy then held the recirculation button and pressed the manual flow contol up arrow. As soon as I did this the left and right temperature displays changed - the left hand one toggles between 8,9,10,11,12 whilst the right hand one (drivers side in UK) stays on 06. No other button combinations affect this, other than recirc + up arrow which stops the process. This behaviour is not as described in the techworld article.

Can anyone make any sense of what the root cause is, or suggest some other tests I can do? I've only had the chance to look at this this evening so have started removing anything (e.g the fan relay) as its dark and cold

Thanks

Dave