expressed precisely :
Ocasionally turning teh AC compressor off and on again sometimes
resets it, as does setting teh temp to LO, but both of these are not a
guarantee to get it funtioning as it should.

I know nothing about the Touran, however...

Could the coil/fins of the unit be freezing up and blocking the flow?

There is supposed to be a sensor on the fins to sense the temperature
and turn the compressor off if they get too cold and start to ice up.
If that sensor has failed or giving a spurious reading...

That would fit in with your turning the a/c off, it defrosting and your
then getting airflow again. Is there a large pool of water appearing
under it, when you stop and after the air flow has dimished?

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk