Dash Temperature Control: Hot or Cold, no inbetween

usersmanual wrote:
there simply has to be a blend door makes no sense otherwise.

When I state Blend door, it is NOT the bottom flap door on the bottom of the Evap housing. That door is to allow outside air to flow over the Evap and heater core. Now, a BLEND door as used on Auto's routes the air thru a series of ducts. This helps regulate Hot and Cold air better. I have been working on Class A heater/AC systems for 37 years and I think I would know the parameters of the systems. Doug