I could be many things from thermostat, control board, wiring, connections, motor, batteries or any of another half dozen items.
unfortunately if it does not happen when a tech is there it comes down to the best educated guess based on the HO input and/or visual clues.
if you have this happen again try turning the thermostat from cool to off, if you have not already, or remove it from the base plate on the wall.
The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
from an excerpt by Paul Jacob in Sun City, AZ