I had the exact same symptoms in my '02 fabia. The temp would get stuck on either cold or hot - mostly hot. It was very dreadful in the summer when the car started putting out lava hot air 😅 And just as you described, even if you put the fan on 0 it would still blow out a small amount of really really hot air.
I took out the v68 motor, cleaned the potentiometer and put it back in and it has been working flawlessly for a few days now (and hopefully will continue to do so). I can adjust the temperatur in small increments and it adapts instantly.
My car is LHD and it was fairly straight forward. You have to remove the center console and i think the left side lower dash (the trim below the steering wheel). The flap motor (v68) is mounted in a plastic bracket and it is a bit fiddly to get it out and very fiddly to get it back in.
Its located here:
I used Hatboy Harveys guides for removing the dashboard:
- The trim below the steering wheel:
- The middle console:
- and then i used this video showing the motor cleaning process (its from a Polo but its the exact same motor and setup). NOTE: In the video the guy recommends using WD40 instead of contact cleaner. I did not do this and used contact cleaner instead.
Additionally i read this thread: https://www.uk-polos.net/viewtopic.php?t=52145 which explains the problem and has some useful images and explanations
If you want to try it i am happy to answer any questions!