is this garbage necessary?

Neal Zimmerman said

I guess another way to ask is how, in all my previous mopars ,(which were all non-ac cars ),and always had a "hot core", what kept heat from continually filling passenger compartment??

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A damper closes when you put the heat selector to cold, and of course the blower wouldn't be on either.

The heater core itself would continue to radiate some heat into the interior without the water shutoff valve.