Ice on inside of windscreen and front door glass
 

Anyone else ever had this? I've never known condensation in car like this before. I had the plenum drain cleaned out in the Summer as that was blocked but I think my car is still taking in water from somewhere.

I used to get this on my old Hilux but expected better in the A8.

Have you checked the aircon drains either side of the transmission tunnel, as they're also prone to blockages.

What about the carpets? Is there any sign of moisture/water under them.

You wouldn’t have a pic diagram of where these are?+++

Look on Audipages for details of the aircon drains, it's a bit of a PITA to get at them. (Or search for Audi A8 orange drains)
Basically they are behind the panels on the transmission tunnel sides, alongside the driver and front passengers calves/knees. So those panels have to come off.
The passenger side is easier and as it's one tray with two outlets just clearing that can work as a short-term fix.

But check under the front carpets first, if they're dry it's a different problem.

This is the Audipages guide, but remember this is for LHD, RHD trims are fixed somewhat differently. http://www.audipages.com/Tech_Articl...tordrains.html
Edit: Sorry, that's the D2 version, D3 is a bit different.

http://www.audipages.com/Tech_Articl...rdrainsD3.html

D3 specific ^^^

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