By slider, do u mean the one below the driver's side vent, that slides back and forth horizontally? Right above the coin tray, also has an outline of a car and an arrow on it... If thats it, just slide it back... Cant remember exactly what its called, but it allows air to come from outside the car... Which would explain why ur heat wont go thru the them... And does sound like a gate opening when u flip it...