blowofff

Generic OBD scanner won't return any fault codes. I had the same issue with my mk3 Fabia, scanned the system with VCDS and found that the recirculation flap is to blame. The PN of the faulty motor in my case is 6R1 907 511 A, however I think it is also sold under PN 8Z1 819 453 B, which also seems to include the flap's housing. I've managed to disassembly it and found out that the potentiometer was full of grease (it is pretty similar like in this video). Cleaning it solved the fluctuation of the fan's RPM. However, don't forget to set the recirculation flap to the same position as the current setting on the climatronic panel, you might end with a flipped function of the recirculation button. The whole process is also described in the workshop manual. You will also need to reset the climatronic after mounting it back.