Ignition "OFF”
Disconnect the connector of mode control actuator.
Verify that the mode control actuator operates to the defrost mode when connecting 12V to the terminal 1 and grounding terminal 2.
Verify that the mode control actuator operates to the vent mode when connecting in the reverse.

Check the voltage between terminals 4 and 5.
Door position  | Voltage (4-5)  | Error detecting  | 
Vent  | 0.3 ± 0.15V  | Low voltage :0.1V or less  | 
Defrost  | 4.7 ± 0.15V  | High voltage :4.9V or more  | 
It will feedback current position of actuator to controls.
If the measured voltage is not specification, substitute with a known-good mode control actuator and check for proper operation.
If the problem is corrected, replace the mode control actuator.