how do I know if the defrost control board versus the main board needs to be replaced? My frigidaire Gallery french-door is not going into auto defrost mode. I called repairman and he turned off power and circuit and said it reset, however after 9 days it was frozen up again. We checked the thermostat and heater and both have continuity. We can put it into manual defrost mode, too. Now he says the main board needs to be replaced? It is very expensive. :(

Hi Rich,
I already replaced the defrost thermostat, as it was a less expensive option, but it wasn't the problem.