Originally Posted by Clavurion

The rear console temperature control (stratified air) thumbwheel is a simple potentiometer. That signal goes to IHKA which operates the rear stratification flap with servo motor on the main HVAC unit. (If the rear blower setting is on zero the basic setting for rear temp is always on warm as a default regardless of the rear temp wheel setting. Reducing cold draft.)

With diagnostics you can check how IHKA sees the temp setting and can activate that servo motor. Like said with simple multimeter you could check if the temp potentiometer is working.

This E39 IHKA document applies to E53 too.

https://dokumen.tips/documents/bmw-e...ng.html?page=1