Genuine Fujitsu 9900727086 Outdoor Dual Thermistor is the thermistor that tells the outdoor unit control board the temperature at the point it is fitted. A failed sensor leaves the board working blind, which shows up as poor heating or cooling, odd cycling or a fault code on the unit. A genuine Fujitsu part is made to the same design as the original, so it goes back in the way the outdoor unit was built.