A silly question but curious: what vent setting do folks use when the AC/heater is off. I ask as for over 10 years of owning different Prius's, I have noticed my cars tend to develop the windshield interior film/haze/glare pretty fast (within two to three weeks of cleaning), whereas cars driven by family members do not. I suspect it's likely due to defaulting to the windshield vent setting all the time (even when using the heater in the winter). I assume using that vent setting obviously pushes air to the windshield leading to a faster buildup of the film/haze/glare on the interior side of the windshield. I am thinking of defaulting to the foot setting (when the AC and/or heater is off), but I am curious what vent setting people usually default to.
Personally, when it's off I turn on the recirculate function, so there is no air at all. The haze is often attributed to offgassing from the plastic in the dashboard and elsewhere in the interior. I'm not sure if this has actually been proven or disproven by anyone.
I agree. The offgassing people say the plastic is getting old and breaking down, giving off other gasses. I haven't come across anyone who has tested the residue to see what it is, though.
The plastics off-gassing idea is very likely what leads to the film/haze/glare, however, we have a Ford Escape Hybrid which doesn't seem to have this issue (though, no idea if we default the vent to the windshield setting). It is over ten years old too. I do "polish" my interior with Aerospace 303, so perhaps that is the culprit (though, it's supposed to improve plastic off-gassing according to detailers)...
For safety reasons, there still IS some air flow, just not enough that you notice. Probably from the floor vents.
Off-topic, but I really wish one of the vent modes was windshield only, not just windshield/heat. I apprecieate if you hit the front defog button that's what you get, but that seems a special case, rip-roaring with auto-AC, not one of the regular modes. And, I'd crawl across broken glass if it'd get me a Prius with ergonomic, eyes-free manual heat/vent controls, but I'll leave that for another discussion, lol.