Abstract: An electronic defrost system consisting of a circuit board designed to implement defrost cycle of an air source heat pump outdoor coil during the off-cycle period. off-cycle is when the house thermostat is satisfied, heat pump is timed off for two minutes and then reactivated in regular defrost cycle if defrost sensor is calling for defrost. (Temp/off cycle). When sensor opens, heat pump will shut off for two minutes to allow pressure equalization. The automatic emergency heat is an option that can be selected. The automatic setting will activate the same circuit as the manual switch at the indoor house thermostat. Defrost control board designed to activate all heat strips during defrost cycle if desired.