Is the air coming from the defroster hot? If it is, coolant, the controller, and coolant reservoir aren't causing the issue. The controller could have failed, but that didn't fix it.
In the system is what is called a mode air door (air distribution door). This door moves to different positions to change the airflow direction. This is where I would be checking.
If you look below, I provided the directions for the removal and replacement of the mode door actuator. I'm not suggesting it needs to be replaced, but it should be checked since it is responsible for where the air exits the system.
Simply remove the actuator motor from the housing and while it is still connected, change the airflow direction to see if the actuator responds.
Try this and let me know what you find.
See pics below.
Images (Click to enlarge)
Thursday, January 13th, 2022 AT 8:25 PM