Genuine Daikin 1259355 Indoor Thermistor is the temperature sensor that tells the indoor unit how warm or cold it is, so it can run at the right level. When it starts to fail, the unit may stop holding the set temperature, blow warmer or cooler than it should, or switch on and off at odd times. A genuine sensor reads temperature the way your Daikin expects, keeping the unit accurate — where a non-genuine part can read off and leave it running incorrectly.