Fujitsu General 18 fault code

What it means

Communication error between the indoor unit and an external device — most often the wireless LAN adapter. Check the adapter is seated and energised before condemning the indoor PCB.

Safety: Safe isolation, then TREAT THE DC LINK AS LIVE. The electrolytic capacitors hold a lethal charge after the supply is off. Discharge through a suitable resistor across the + and − terminals and confirm with a meter on DC before touching the board. Never short the terminals with a screwdriver.

Source: Fujitsu General ASEH07/09/12/14KMCG service manual (official UK webstore), error-code table + troubleshooting; cross-checked against SR_AS092EF_01. All 23 codes verified model-specific 2026-07-16.

UK models this code applies to

Tap yours to open 18 on that machine.

18 on these comes from each model's own manual, which may not match the meaning above — tap yours to read it.

Now the harder half: proving what caused it

18 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.

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