Fujitsu k9900878009 Middle Heat Thermistor

Product Description

The FUJITSU k9900878009 is a middle heat thermistor designed for use in Fujitsu mini-split outdoor units. This temperature sensor monitors heat exchanger coil temperature at a mid-point location, providing feedback to the system control board to regulate compressor and fan operation. It is a direct OEM replacement part installed by licensed HVAC technicians servicing Fujitsu ductless systems. Proper thermistor function is critical to system efficiency, defrost cycle accuracy, and protection against compressor overload conditions.

This thermistor is used in Fujitsu outdoor condensing units in residential and light-commercial ductless mini-split applications. It mounts to the middle section of the heat exchanger and feeds temperature data to the main control board. Compatible outdoor unit models include AOU18RLXFZH, AOU24RLXFZH, and AOU36RLXFZ1. Replacement is typically required when the system throws a thermistor fault code or exhibits erratic defrost or heating performance.

Key Features

• OEM replacement thermistor for Fujitsu outdoor mini-split units
• Monitors mid-coil heat exchanger temperature for system control and protection
• Supports accurate defrost cycle initiation and termination
• Direct fit for specified AOU-series outdoor unit models
• Compact form factor for straightforward swap-out replacement

Compatibility

Compatible with Fujitsu outdoor units AOU18RLXFZH, AOU24RLXFZH, and AOU36RLXFZ1.

Installation Notes

Installation should be performed by a licensed HVAC technician familiar with ductless mini-split systems. Disconnect power to the outdoor unit at the disconnect box before removing or installing any sensors. Ensure the thermistor connector is fully seated and the lead wire is routed away from sharp edges or moving components. Consult the unit wiring diagram and service manual for connector location and fault code diagnostics.