I am not getting heat out of the dash vents on auto

My 2005 lincoln town car hvac will not blow warm air out of the dash vents in auto. When select manual dash vent it takes a long time for the air to start coming out. This is with the car warmed up and driving normal operation and is repeatable. Please help when the dealer did diagnosis, they told me it is normal on auto not to have warm air out of dash. They said warm air rises and system design is to put out warm air at floor so it rises. Also design for cool air to come out of dash as cool air falls. Ok I get the physics. But even if the delta temperature is 50 degrees? And what about the fan speed at 50o being full speed all the time? It does slow down with lower delta. Even on auto the fan speed is on full without warm air at times. Another symptom is when manual floor vent selected, warm air comes out of defroster.