I experienced the outside flap not opening as well, but then when I turned DOWN the Maxx fan, it reverted to normal operation and worked. I believe the Maxx fan was creating a bit of a pressure difference that the hood fan couldn't overcome. There were no windows open.
2009 Tacoma Crew Cab, TRD 4WD
2007 Tundra Double Cab TRD 4WD
2014 Escape 19
2007 Norwegian Elkhound "Baxter"