smoke from interior air vents when air con is on!

[alastairm]

Does anyone know what causes this or how to fix it? Seems to happen when the air con has been on for 30 mins or more and then i get smoke coming into the interior until i switch it to 'econ' mode which stops the smoke almost right away.
Is it drain holes? Where should i be looking in order to track the problem down?
Thanks

[nekrum]

I've had this too but only on a long run 1h 30min +, still not got the bottom of it?!.. Had it checked with VAGCOM and I had a Air Quality sensor fault (by the air filter) which was replaced.. Not done a long run since so I'm not sure if it has cured it but is interesting that yours does it a lot sooner than mine did?!.. If anyone has any thoughts on this I would also be interested..