When I push the Auto button for the AC the airflow defaults to the dash vents only. Is there a way to make it default to the dash and floor vents?

 

It will always default to the dash settings when it's hot. You can always change it by touching the climate button on the dash and then touch the screen how you want the air to flow...

Craig

 

The problem, if it can be called that, is there are sensors situated arbitrarily thoughout the cabin, and these control the solenoids that open or close their respective vents. I find the firing pattern strange at times as well, but that is probably because of my own geographical location, compared to the way the car's HVAC is set up to begin with. There is also a sun sensor that triggers a blast of cool air from the upper vents whenever the front of the car is exposed. Generally, the upper half of the cabin gets the most and the coolest air because hot air accumulates there. Short of adjusting the control the way Craig has helpfully suggested, you could lower your upper vents or reduce the airflow there; however, you will lose the smog sensor's ability to filter out fumes from the outside as this function only operates on Auto.

 

The Lexus gods have spoken, and the upper vents are all you will get in Auto mode.