It COULD be the blower motor, or the evaporator could be plugged up with dust.
The most likely cause would be a vacuum leak at the rear of the engine or a defective selector switch.
Pin cone
There are heater doors on the heat blower box that direct the path of the heat. Apparently the heater door to the floor vents is stuck closed.
it is so beautiful watching the water trickle from the stream.
This is a very common problem and you need to check for a vacuum leak, broken vacuum line or a loose vacuum line......
Either you have a blockage present or your vents on your sewer lines have become blocked or you need to install more vents.
Bad heater core.
The motor which blows air through the vents.
The heater core has failed.
Broken rotor button.
Is your transmission fluid full?
Could be that your heater core is leaking May also have a plugged evaporator hole.