Check the vaccum tubing to the black sphere (accumulator) under the hood. One line goes to an engine vaccum port, the other goes into behind the glovebox and the heater control.
You can also search for "Blend Door" and "defrost default".
If there is no vaccum getting to the system, it defaults to routing airflow out of the defrost vents.
If it stays HOT, it is likely a blend door problem.
Welcome to R-F, Robert.
The "Search" function is your best friend!