2007 lexus es 350 and the drivers side heat with dual climate control blows cold. no coolant leaks, fluid level is fine, engine gets to temp by way of gauge fine, system switches to selected vents fine, air flow to both sides is the same, and I can hear the heat flow servers moving when I adjust the temperate up or down. but nothing I do will get me heat on drivers side vents--all of them. passenger side works fine. please help