The airflow direction on this vehicle is controlled by a mode door. On many vehicles, there is an electric motor that opens and closes the door to change airflow direction. On this truck, it is controlled by an engine vacuum.
So, does it respond quickly when you change from floor to defrost? If it does, the mode door vacuum motor could be bad, there could be a vacuum leak, or the vacuum hose may have broken or come disconnected.
I attached a pic below. Number 1 in the pic is the mode door motor in question. Check to see if it is connected and getting a vacuum when you select the panel.
Let me know what you find.
See pic below.
Image (Click to make bigger)
Thursday, August 25th, 2022 AT 7:14 PM