Codes 31 and 41, A/C control assembly totally off?

The climate control panel is totally off and there is no function. I checked all fuses and heater relay, that's okay. I changed the control unit, and the display worked for a short time but then it seemed to damage. The runtime check gives me error code 31 and 41, what should be the air mix servomotor, which makes noises and could not move. So, I removed it and tested it with a power adapter and without load it runs good. I also checked the blower motor, and it runs also good. But why is the control unit two times damaged? At the connector pin 13 and 24 is 12, 6V. So, it should power on, but it seems that something has a shorts circuit and damages the unit. What tests can I do with the connector to find the issue?