I hear a loud clicking noise coming from under my dash when I start the truck.
All of the controls for your heating and AC are controlled by electric actuators; they move “doors” to control the airflow and temperature. When you start your truck, all of them go through a self check; from your description, it sounds as though you have a problem with one of them. The blend door actuator is a common repair for your truck. You have two of them if you have driver, and passenger controls for temperature. I recommend having a certified technician, such as one from YourMechanic, come out to your truck’s location to inspect your AC system, and recommend the best path to repair.
Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing