Air conditioning control off - no blower

[oscarmeier]

Hello, I have an error with the air conditioning control: The control panel fails and can not be started reliably - however, I have already connected another, which behaves the same. When it is on, the adjustment of the servo motor for the air flaps (position output) can also be heard and the start-up of the air conditioning is audible. The servo motor on the driver's seat for the air flaps (heat control) has cracked and stuck - I have already removed it and it can be turned with a power supply and also provides realistic resistance values from 800 Ohm to about 6kOhm. If you turn on the ventilation at the control panel a relay clicks, but the fan stays off. The fan itself can be turned with a power supply and the series resistor has already been replaced. All fuses had continuity, however the control panel does not run stable. I could imagine a cable break or a bad power supply. But now I don't know how to check the wiring harness systemically, i.e. on which wires must 12V be present for the air conditioning control and on which wires does the control of the motor come out? Why does the control panel flicker? Do you have any ideas?