Safety first: Disconnect power before accessing the indoor coil area. Coil fins are sharp; wear gloves.

Locate the coil thermistor: Remove the front cover and swing down the blower assembly if required. The coil thermistor is usually clipped to the evaporator coil tubing or fins.
Check mounting: Ensure the thermistor is firmly clipped to the coil surface. A loose sensor can misread temperature and trigger E3. Reattach securely.
Inspect wiring: Follow the thermistor wires back to the PCB. Look for pinched, cut, or corroded wires. Repair or replace the harness if damaged.
Resistance test: With power off and the sensor unplugged, measure resistance. Compare to Fujitsu specifications for the current coil temperature. Replace the thermistor if readings are far out of range or intermittent when you gently flex the wires.
Reset and test: After replacing or reseating the sensor, restore power and run the unit in cooling and heating to confirm the error is cleared.
PCB replacement: If multiple new thermistors still cause E3, the indoor PCB is likely faulty and should be replaced by a qualified technician.

Unit stops cooling or heating, E3 error indicated, fan may continue running

Possible Causes