When the bus is moving a surprising amount of cool air comes in through the dash and defroster vents even when the blue levers are shoved into the fully upright and locked position. I can't figure out why this should be. The flaps behind the front grilles open and close as they should and I see rubber on them flaps.
What's the Collective Wisdom on this? I could seal the flaps with duct tape and see if air is still venting in. A good place to start?