Originally Posted by charliemike

Everything should be closed. The sunroof creates drag because of the wind coming into the opening. That wind coming in has to displace whatever air is inside the car or you'd be crushed by the compression.

So, using my deductive powers and TruLogic® reasoning prowess I'm assuming that the outside air is forcing the cooler inside air out through all the seams and holes inside. The recirculating feature of modern HVAC systems in autos is probably far more efficient than blowing A/C into a car with open windows/sunroofs (is it roofs or rooves? LOL)

Or something.