Carrier TC-NAC Owner's Manual page 6

BUTTON IDENTIFICATION
a. FAN
Selects whether the fan operates continuously (on) or only when
needed for heating or cooling (auto)
b. MODE Selects whether thermostat is set for heating, cooling, emergency
heat (heat pump system only), auto (heat and cool as needed), or off
c. UP
Increases the temperature or adjusts the screen selection up when
setting advanced features
d. DOWN Decreases the temperature or adjusts the screen selection down
when setting advanced features