Who gets priority—the one who wants the window open, or the one who wants it closed?
If people in the same room disagree over opening or closing the window, or turning the air conditioning on or off, they should abide by the following guidelines:
In the winter, a single individual can prevail to have the window or the air conditioning closed or have the heat turned up. The same principle applies in reverse: in the summer, the one who wishes to open the window or turn on the air conditioning prevails, even if someone might catch a cold.
In the spring or fall, when it’s not very cold or very hot, those present should either come to a consensus—since both groups have equal say—or follow whatever is customary for that climate.
If one of those present is already unwell, their needs take priority, regardless of the season.
If the person who is cold has the option of wearing a sweater or coat, they should do so before making any demands; if they’re still cold, then the above rules should be followed.
Even if the halachah is on their side, one should strive to be mevater (yield to others), since making peace is the vehicle for receiving Hashem’s blessings.