Is this my actuator?? W900

The dam blend door has a way of breaking.
Older trucks you had to take the whole dash apart to get at blend door.
Duck tape your fresh air inlet to keep the outside out in a pinch.

 

The T680’s is on the top and requires the whole dash to be pulled. I’m not sure what all components, if any, are shared between the trucks, though.

 

What year is your truck? Some newer vehicles do use the blend door to control temp. Here is a link with some good diagrams.
Blend Door and Blend Door Actuators: What to know — Ricks Free Auto Repair Advice Ricks Free Auto Repair Advice | Car Repair Tips and How-To Advice
Do you have a heater control valve? Check your heater hoses at the firewall. It may be that it is not always responding to the dash control.

Electrical Issues: Since actuators rely on electrical signals, problems like blown fuses, faulty wiring, or a malfunctioning climate control module can prevent them from working.

Encoder Sensor Failure: If the actuator’s position sensor fails, the climate control system won’t know the door’s position, leading to erratic temperature control.

 

All the actuator does is move the blend doors.
Their should be 3 of them on your truck.
1 defroster vent
2 foot and dash heat and cool
3 blend door

 

Sorry, i can't remember exactly which one that is. Did you try manually moving the door to make sure it wasn't the correct one?

Also, are you sure it's a door? Don't you have a heater control valve under the hood, right side of firewall?

 

If I remember right the defroster one is on top
The dash foot is right next to heater motor and hot colt id bottom right side