In vagcom aka vcds, on an 8P anyway but check yours aswell, there's a basic setting in hvac module 08 that actually tests the unit & sets it up as if were new, think was 001 with vagcom, give it a go & see what you get back as if its a flap then should show you which one like V153 etc, but staz is right, the main unit is housed behind the center console & it spreads across to the passenger side behind the glovebox, the main center unit usually houses the motors etc for flaps, although there's 1-3 actually on the part behind the glovebox, but its tad tight in there to get to & I unfortunately have a similar job to upgrade my climate at some point, not fun at all especially in winter.
Let us know what vcds reports as it might just need recalibrating to resolve.