AC operation question about recirculation

[Mikl777]

I am doing some troubleshooting and repair on my ac system. The manual says that when the controls are set at: dial=min pushbutton=max blower=auto the air is 80% recirculated. The manual also says that the outside air duct defaults to the closed position.
My question: If the outside air (main air actuators) are closed would there be 100% recirculated air or does the 20% outside air come in from another source.
The reason I ask is because I live in Las Vegas where it gets very hot. I would like to have 100% recirculated air to improve the cooling in the car. If the fresh air comes in from the main air flaps I will try to disable it at least for the summer. If it comes in somewhere else does anyone know where that is and if it can be closed off?
Thanks
Mike A
1985 Black 380SL