What could be going on with my HVAC?
What the Dr. Mentioned will be located outside by the air conditioner and not in the settings. Count the boxes at the air conditioner. One is the disconnect for the air conditioner. If there is another then that will probably be it.
However I do wonder, does the furnace sense air flow? As in filter clogged.
Best thing is refer to the manual for your model of furnace to see if it indicates error codes.