Anyone know what this thing is?

tonysrt said

There is a "control chart" in the AC section that shows water valve is closed in all AC positions regardless of whether AC or Max AC.

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If it worked as you describe it would not be possible to affect (warm) the air out put when AC is selected. But one can affect the cold AC out put by using the Temperature Control lever. The Temperature Control lever blends in air that has passed through the heater core. Only on Max AC and when the system is Off is the water to the heater core blocked.