Genuine Daikin 063155J Outdoor Coil Thermistor is the temperature sensor clipped to the outdoor coil that tells the system the coil temperature, so it can run correctly and manage defrost. When it starts to fail, the outdoor unit may lose output, ice up or defrost at the wrong times, or stop and start unexpectedly. A genuine sensor reads temperature the way your Daikin expects, keeping the system accurate — where a non-genuine part can read off and leave it running incorrectly.