Genuine Daikin 128855J Indoor Thermistor Assembly is the temperature-sensor assembly that tells the indoor unit how warm or cold it is, so it can run at the right level. When it begins to fail, the unit may stop holding the set temperature, blow warmer or cooler than expected, or cycle on and off at the wrong times. A genuine assembly reads temperature the way your Daikin expects, keeping the unit accurate — where a non-genuine part can read off and leave it running wrong.