^^^ THIS
I have never been able to figure that out either. We never, ever ride the bus unless we are forced to in such situations as riding to HDDR. Although now we just park at the Wilderness lodge and take a boat to HDDR. We rode the bus there once and the driver had the AC on so cold it was (no joke here) just like a meat locker. The windows actually had condensation on them. There were two elderly looking ladies among all the freezing people and they looked like they were going to die. Shaking, shivering, and huddled together. I finally asked the driver to turn the AC down and he actually refused saying "It will get too hot if I do. No one else minds the air."
I told him that if it stays like this for much longer we're going to start feeling like the Donner party. Unfortunately, I think we all took the purple bus that night and not the yellow one. (There are three. One is a very long ride and the others are shorter)