Upon arrival heat pump was working properly, activated defrost successfully, issue with cooling mode came around when customer got back from trip and they had to turn thermostat back to heating mode. When they turned thermostat back to heating mode auxiliary heat turned on because they set thermostat temperature 3 degrees above room temperature. Customer was not informed about aprilaire thermostats activating auxiliary heat when temperature is raised more than 1 degree above room temperature. Told customer to see if thermostat acts up again and we will replace thermostat free of charge System is heating at this time