We can only get heat from the defroster and on the floor. Can't figure out how to get it to come out of the vent. We've already done alot of work on this vehicle. We went right thru it. Flushed radiator, replaced water pump , replaced gaskets on valve covers. Flushed coolant system and heater core. Just can't get the heat to come through the vents. To be honest, I can't even figure out the controls on the dash to direct the heat to the vents! Please help. Thank you