my heater turns on and blows hard on defrost but I switch to upper vents and it's still blowing but not out the upper vents or floor vents, pretty sure it's not coming out anywhere in the cab, so what could be my problem?

 

Blend door probably broke or stuck or a vacuum leak to the actuators. We refer to them as Daks.

 

where is the blend door? bc I just replaced the blower motor and the only thing I seen was the cover over the blower motor had a little door on it

 

The blend foods are in or under the dash, inside the ducting. They direct airflow depending on position.