well,tom , I knew that the turbine role it's to cool the air.It's not like the engine turbine,which is driven by the airflow and is conected to the fan.
The turbine from the pack must rotate and cool the airflow.It is not a free turbine.Also the compressor.
It's like talking about a propeler,if it's rotated by the forward movement of the plane or by the engine and thus moving the air backwards. Of course,it's actionated by the engine.
The temperature selector regulates the airflow through the pack ACM,as you said by means of a mix valve.
The airflow is as demanded,if you select high flow,the compressor will go faster,sucking more air from engine bleed.