This is a Cavanaugh Auto Changeover dbl stage regulator
which is an improvement over the older styles because it allows you to remove an empty cylinder without gas bleed-by
The center dot (Red /Green ) indicates empty/not empty for which ever tank the selector valve is open to. The Red position is for curb side tank on my unit and the green for the other one. If you open the tank that is selected, the red dot should change to Green. btw they are not LED's. It is a passive device that reacts to the LP pressure (and liquid xtal matreial.. I think).
It will automatically switch to the full tank when needed. But the valve does not swith the gas flow...It only swithes which bottle is connected to the colored indicator. This always confused me.!
btw...I did read this somewhere in the stack of stuff they gave us with our unit, but I can't remember where now. (Not in the palomino manual)