Fujitsu 84.1 error code

What it means

Fujitsu's outdoor board shows these dot-decimal codes only after an error is active: the red ERROR LED blinks at high speed, then a brief SW1 press makes the MONITOR LEDs blink out the code. Code 84.1 means the outdoor unit cannot trust the heat sink temperature sensor reading. That reading protects compressor, inverter, pressure, or refrigerant-flow control.

Urgency

Likely causes

1. Dirty filters, blocked coil airflow, or an outdoor clearance problem increasing pressure or temperature
2. Low charge, overcharge, leak, or refrigerant-flow restriction
3. Discharge, pressure, or refrigerant sensor reading outside range
4. Compressor, valve, or outdoor board issue after airflow and charge are verified

Homeowner fix

Turn the system off with the remote, then power cycle once at the breaker or disconnect only if you can do that safely. Expected result: a temporary control lockup clears; if the same code returns, stop resetting and schedule service. Do not remove outdoor panels or unplug sensors.

When to call a pro

Call a licensed HVAC technician if the code returns after the safe reset. Tell them the exact Fujitsu SW1 code is 84.1 and the Section 14-3 meaning is: Heat sink temp sensor error.

Repair vs replace

Sensor faults are usually repairable. Compare repair with replacement only if several sensors, an outdoor board, or a major refrigerant/compressor repair is quoted together.

• Fujitsu AIRSTAGE H-series Compact Cassette 9,000 BTU R-32 208/230V (ACUH09KUAS / AOUH09KUAS1)

  AIRSTAGE H-series

• Fujitsu AIRSTAGE H-series Compact Cassette 12,000 BTU R-32 208/230V (ACUH12KUAS / AOUH12KUBS1)

  AIRSTAGE H-series

• Fujitsu AIRSTAGE H-series Floor-Mounted Console 12,000 BTU R-32 208/230V (AGUH12KUAS / AOUH12KUBS1)

  AIRSTAGE H-series

• Fujitsu AIRSTAGE H-series Mid Static Duct 12,000 BTU R-32 208/230V (ARUH12KUAS / AOUH12KUBS1)

  AIRSTAGE H-series

Parts for this line

The parts catalog for Fujitsu AIRSTAGE H-series lists 6 sourced replacement parts for this product line.

For your technician

Technician note: Section 14-3 lists 84.1 as Heat sink temp sensor error; verify sensor placement, resistance, connector condition, harness continuity, and outdoor PCB input before replacement. Page context: Fujitsu maps this display to the AIRSTAGE H-series line; source: Fujitsu AOUH18-45KWAS/KWAH R-32 Design & Technical Manual; display convention: match the eighty four and one marker exactly before comparing neighboring codes.

Which systems show it

• Fujitsu Halcyon/AIRSTAGE R-32 AOUH18KWAS2, AOUH24KWAS3, AOUH36KWAS4, and AOUH45KWAS5 outdoor-unit manuals where Section 14-3 lists the same SW1/MONITOR error-code table.
• Fujitsu AOUH18KWAH2 and AOUH36KWAH4 XLTH sibling design manuals where the extracted Section 14-3 table matches the KWAS manuals.

Related troubleshooting

Use the symptom guide alongside the exact display code if the unit is flashing, cycling, or showing comfort symptoms.

Reset note

Turn the system off with the remote, then power cycle once at the breaker or disconnect only if you can do that safely. Expected result: a temporary control lockup clears; if the same code returns, stop resetting and schedule service. Do not remove outdoor panels or unplug sensors.

Manual trigger

Fujitsu's outdoor board shows these dot-decimal codes only after an error is active: the red ERROR LED blinks at high speed, then a brief SW1 press makes the MONITOR LEDs blink out the code. Code 84.1 means the outdoor unit cannot trust the heat sink temperature sensor reading. That reading protects compressor, inverter, pressure, or refrigerant-flow control.

Related codes

Source

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