ActronAir Outdoor Coil Defrost Sensor 1.9m monitors outdoor coil temperature for defrost management on Classic Series and ESP Plus residential split ducted systems, using a 1.9-metre cable that provides greater reach than the standard 1.2m sensor for outdoor units where the PCB is positioned away from the coil sensing location. A failed defrost sensor causes either continuous defrost operation or no defrost -- both conditions result in progressive capacity loss in heating mode and must be rectified promptly in cold weather. Isolate power at mains before replacing any outdoor defrost sensors.