Warm(er) air rises - if vents were high up there would be little circulation without fans.
on the floor on the floor
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.
should be on floor.
yes
Heating vents should be placed near or on the floor in a room because heat travels up not down.
the middle vents only supply air from the ac unit using a separate in dash fan. the floor and defrost vents come only from the heater
Ceiling. Cold air fails
radiation
Most likely a bad or disconnected vacuum hose to the defrost/floor selector in the heater ducting.
because warm air rises.
Heating vents should be placed on or near the floor because heat rises. In rising, it will warm the air of the room. If the heating vent were near the ceiling, the room would stay chilly, even though heat was being poured into it.
Heating vents should be located near the floor since hot air rises. If the heating vents are located near the ceiling the heat would stay there and not warm the room.