Unit stops with E6 error, often during heating defrost or low ambient operation

Safety first: Turn off power at the outdoor disconnect. Outdoor coils have sharp fins; wear gloves and eye protection.

• Locate the coil sensor: The outdoor coil thermistor is typically clipped to the coil tubing or embedded in the fins near the middle of the coil.
• Check mounting and cleanliness: Ensure the sensor is firmly clipped and not buried in heavy dirt or ice. Clean the coil gently with a soft brush and water if heavily soiled.
• Inspect wiring: Trace the sensor wires to the PCB, checking for pinched or cut insulation. Repair or replace the harness if damaged.
• Measure resistance: With the sensor unplugged and coil at ambient temperature, measure resistance and compare to Fujitsu specs. Replace the thermistor if readings are out of range.
• Reassemble and test: Reconnect everything, restore power, and run the unit through a full heating cycle to ensure no E6 error returns.
• Board fault: Persistent E6 with a new sensor suggests a defective outdoor PCB, which should be replaced by a technician.