This might be a stupid ? but I think my heater dosnt work how its supposed to. I know that if you put the top slider half way thats the defrost setting. and with mine if i slide them both to the right it just comes out by my feet. What is it supposed to do if you pull the bottom knob out TWO times. Mine NEVER comes out of the top vents. Can someone just explain how a full functioning 620 heater is supposed to work?