Plateau Sprinter heater question

[VanGoGirl]

We have a 2011 Pleasure-way Plateau Mercedes Sprinter. My question is about the heater in the cab. The A/C works fine, as does the defroster. But we have yet to figure out how to get heat coming on our feet. There is a round dial on the dash, which we turn so that the white dot is at 6 o'clock, and we close off the dash vents. Can some owner tell us what we're doing wrong? (After 8 years!!)