Where I live I rarely need AC, so I usually run in the EC mode. In EC with the temp set to give warmed air, pressing the blue button gives cooler outside air from the center vent while still getting warm air to the other vents. Pressing the red button gives warm air to the center vent, and un-pressing both gives no air to the center vent. I like to have heat on my feet and cool air in my face, so in winter, I usually drive with the blue button on and I set the side vents to minimum.

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Resistance is Futile.