For reference, the very common Honeywell thermostats that seem to be in every US house built in the last 20 minutes just have an unmarked button that cycles bet

For reference, the very common Honeywell thermostats that seem to be in every US house built in the last 20 minutes just have an unmarked button that cycles between Auto, Off, Heat, and Cool. (Auto means Heat/Cool.) It does have the advantage that there are only four buttons on the whole unit, so trial and error works pretty well.