* Partial Recirculate Mode. The Leaf has a barely-documented feature that is actually very helpful in Winter, especially when combined with the next Trick after this. With the ventilation set to one of the modes that allows Recirculation (any of the non-defrost modes), and with Recirculate mode on, press and hold the Recirculate button until the light above it starts to flash, then quickly release it. The light will flash twice, then go out, making it look like the car is in Fresh Air mode. In fact, if done correctly (and it may take a little practice, to avoid re-engaging full Recirculate) the ventilation system is now taking in roughly 1/3 fresh air, and recirculating the other 2/3. This mode does two things: it reduces the amount of external smog getting sucked into the car, and it increases the efficiency of the heater in cold weather, because most of the air doesn't have to be heated from outside ambient. It is also called "Auto Recirculate" (not to be confused with Auto Climate Control).
If the valve does open and close automatically, what are the parameters that determine an open position? They are unlikely to be present only in Summer. Once I have more info I'll change it to reflect that.