I see there is a sort of valve on the engine compartment, with a vacuum line connected to it. Looks like it would restrict coolant flow maybe when the AC is On? I know the vacuum will switch the valve but where is the control switch or trigger?
I'll take a pic if necessary.
Thank You.

 

That valve is closed when the "off" or "max A/C" buttons are pushed. The vacuum switches are in the control panel.