Blower motor always on!

[Telefragged]

Recently the blower motor on my 96 A8 has started acting up and refuses to blow at any speed other than maximum while the ignition or engine is on, even when the AC control unit is set to off. At the moment I've worked around this by removing the fuse from the yellow row, column 5.

Now before all this I had no ambient temperature on the instrument panel display, but after pulling the fuse it now shows a constant -27C which told me the ambient temperature sensor was failing. The problem persisted after replacing the G17 ambient sensor behind the bumper. With the fuse back in place the car is as before (Blower motor always on, no ambient temperature on display).

The previous owner replaced the dashboard with the facelift version including the AC controller. The instrument cluster is still the preface version. Could there be a mismatch with the connection between the AC controller and the instrument cluster?

I got 3 error codes from the HVAC system:

01317 - Instrument Cluster (J285): No Communications
01273 - Fresh Air Blower (V2)
01314 - Engine Control Module: No Communications