This means that during the winter I must select either the floor / defrost mix , or the vent position , both of which work as intended . I ' ve managed to survive two upstate NY winters with the heater in this state of disrepair . It requires next to no maintenance , and what it requires does n't cost very much .

Question: what is the reason I must select either floor / defrost or vent position ?
Answer: The manual says there is a rule regarding vents .The heater will over work and short out .There is a part malfunction because you should be able to set BOTH the vent direction and select a heat setting .None of the above choices .