Haasman,
ok i tried what you asked. and here's what I found.
with the a/c on and circulation mode on as well, yes the light for circulation does come on and i do hear the flips working to go into recirculation mode. with the a/c on all the time when the temp control is on cold mode it's all good, with the same exact setting, circulation on, a/c on, when i turn the wheel to the hot setting the headache comes back.
and yes, that's what i've been wondering all along as well, i'm not sure whether there's a seperate (fresh air) vent that works while the temp control knob is on the heat mode. because that's what it feels like as if the fresh air just vanishes when the heat is turned on, and when the temp is set back to cold i can literally smell the cold fresh air breeze come in again.
so does this make any sense so far ?

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