Does the vehicle have the automatic temperature control system in it?
What does the temperature gauge read?
The problem is the blend air door inside the heater and a/c box. It is not moving. You need to see if the motor is moving when the switch is changed from heat to a/c. You can remove the motor then turn the switch to see if it moves. If it moves the door is broken inside the housing if it doesn't move then the motor is bad or not getting power from the control head ( so test for voltage if it doesn't move). If there is voltage then replace the motor, if no replace the control head.
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