Ignition "OFF".
Disconnect the connector of temperature control actuator.
Verify that the temperature control actuator operates to the hot position when connecting 12V to the terminal 1 and grounding terminal 2.
Verify that the temperature control actuator operates to the cool position when connecting in the reverse.

Check the voltage between terminals 4 and 5.
Door position  | Voltage (4-5)  | Error detecting  | 
Max. cooling  | 0.3 ± 0.15V  | Low voltage : 0.1V or less  | 
Max. heating  | 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 temperature control actuator and check for proper operation.
If the problem is corrected, replace the temperature control actuator.