it controls the flow of air from the vent in the middle of the dash in conjunction with the thermostat. if you turn it to all blue dots, lots of cold air will come out of that vent as long as you have selected cold air on the 'stat. If you turn it all the way to red, only hot air will come out.
Member of the "Pie Eating, Beer Swilling, Porn Watching, Ball Sctratching" club. And proud of it.
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