There isn't one! I just in the last few days started using some air from time to time, and a quick glance at the dash controls showed a button with something about max air, and as my Ford pickup has just such a air con control I pushed it for what I thought would be a quicker cool down.
Some where over the next few days I realized pushing that button would not result in more cool air, and as I was already using the recirc function and of course the main air button, didn't sweat it, sorry for the pun, but was keeping plenty cool. Then I realized that button is for the rear window de fogger, and that explained it! In my defense, I drive another rig in the winter, so I don't think I ever used that button for it's intended purpose. Also, the lettering by the button says MAX AIR, and then has a little ilustration of the recirc or flow through control, so it is a bit misleading. Sure it also has an illustration of a rear window with heat shimmers, but it could be construed as the windshield getting colder. It sucks getting old

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