Carrier Performance Non-Programmable ADGE Owner's Manual page 36

Outdoor
temperature display
The thermostat automatically displays the outdoor temperature when you press the
features button.
Auto changeover
The thermostat displays one of five modes: hoar, cool, Em boat (heat pump
version only), boat cool (auto mode) and off. When the mode selection is for both
heating and cooling - auto mode - the thermostat is in auto changeover mode. This
allows the system to switch from heating to cooling - or from cooling to heating -
to maintain the temperatures you've programmed. It does this automatically.