S3 8V HVAC no fresh air, but no fault codes

[audivi]

I have a problem where the HVAC remains on recirculate regardless of setting of the recirc button. All airflow is otherwise normal from vents, fans working. VCDS shows no fault codes so there is no apparent problem with the pollution sensor or flap motors. Changing the cabin air filter made no difference (no surprise).

Any suggestions on where to look next?

One vaguely possible suspect is a faulty sensor, not failed but always giving the wrong answer. Does the sensor have a known expected lifetime? I am not keen to replace it on spec.

Another might just relate to using cooling rather than heating, although I have no idea what actual connection might exist. I mention it only because the problem first appeared late last Summer, disappeared over Winter, and reappeared last weekend.

Does the sensor sit ahead of the heat/cool function or after it?

[MIG]

I had a similar issue on my Bora; the air was stuck on recirc no matter what. I found that the flap had snapped off the motor, so the sensor on the motor still thought it was opening and closing.

I found it by pulling the air filter out and you could watch the flap; while doing a VCDS output test on the flap, it made the noise but no movement.

I did not fix it in the end, it was too hard to pull the whole airbox to fix it, but I did manage to force the flap open for some fresh air


Edit, or are you saying the light\button won't switch off recirc mode?

[audivi]

I think you may have it exactly, MIG (the main part, not your edit comment). A broken connecting arm would account for the lack of either actions or fault codes. From videos, they appear to be colourful bits of plastic for the various motors and flaps.

I will check the manual and videos on getting a closer look.

Thank you for your comment mentioning your experience.