Fujitsu Mini-Split: 1 Flashes
A Fujitsu mini-split LED pattern starting with 1 flashes matches 4 documented codes: 11, 12, 15, 18. Watch the full pattern (short vs. long flashes) to tell them apart — all 4 are explained below.
Code 11: Serial communication error
Serial communication error. At start up the indoor unit (evaporator) and outdoor unit (condenser) are not talking to each other over the communication wire, so the system will not run.
Manual wording: “Communication Error - At Start up, evaporator and condenser are not communicating.”
Documented for: RL2, RLS2, RLS3, RLS3H, RLS3Y, RLB, RLXB, RLXEH, RLF, RLF1, RGLX, RLE, LUAS1, LMAS, LZBS, LZAS, LPAS series
Likely causes, most common first
- Bad or loose interconnecting wiring between the panel, condenser and evaporator (wire nuts and splices are not recommended by Fujitsu)
- Incorrect voltage at the panel, condenser or evaporator
- Open, shorted, or mis-landed communication conductor
- Failed indoor or outdoor control PCB
What you can safely check yourself
- Check that the breaker and the outdoor disconnect switch are both on
- Turn the system off at the breaker for about 5 minutes, then back on, and see whether the code returns
When to call a technician
Everything past a power reset on this code is line-voltage and communication-wire work at the disconnect, condenser and indoor unit. Have a licensed technician check the wiring and voltages.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25
- Communication Error - Fujitsu General Help Center (Fujitsu General America, Inc., RL2, RLS3, RLS2, RLB/RLXB, RLF, RLF1, LUAS1, LMAS, LZBS, LZAS, LPAS, RGLX, RLE series (plus legacy series patterns)) · checked 2026-08-25
Code 12: Wired remote controller communication error
Wired remote controller communication error. The indoor unit has not received a signal from the wired wall controller for more than 1 minute during normal operation.
Manual wording: “Wired Remote Controller Communication Error - When the indoor unit cannot receive the signal from the Wired Remote Control for more than 1 minute during normal operation.”
Documented for: RGLX, RL2/RLS3/RLB/RLXB wall mounted, RLF/RLF1 multi-zone indoor units
Likely causes, most common first
- Loose or disconnected terminal between the wired remote controller and the indoor unit
- Broken or damaged remote controller cable
- Failed wired remote controller
- Failed indoor controller PCB
What you can safely check yourself
- Turn the power off at the breaker for about 5 minutes and back on to see whether the code clears
When to call a technician
The remote controller cable lands on the indoor unit's control board terminals. Checking or reseating it means opening the electrical cover, which is a technician's job.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25
Code 15: On multi-zone
On multi-zone (RLF/RLF1) systems: check-run unfinished. The installer's commissioning 'check run' was never completed, so the system refuses a run command from the remote. On RGLX ducted/cassette models the same pattern means automatic air flow adjustment error (the indoor fan could not complete its airflow learning routine).
Manual wording: “Check-Run Unfinished - When the operation command is inputted by the remote controller without check operation completion.”
Documented for: Multi-zone: ASU7/9/12RLF1, ASU18RLF, ASU15RLS, ASU15RLS2, ASU15RLF1, ASU24RLF, ARU/AUU/AGU RLF series, AOU48RLXFZ (E156). RGLX: AUU/ARU 12-48RGLX
Likely causes, most common first
- Multi-zone: the check-run commissioning procedure was not completed after installation
- Multi-zone: wrong indoor unit count connected, or an indoor unit was powered on part way through check run
- RGLX: indoor fan caught, obstructed, or the motor is locked
- RGLX: excessive ambient temperature around the indoor fan motor
What you can safely check yourself
- Make sure the return air filter is clean and the supply and return grilles are open and unobstructed
- Turn all indoor units off with their remotes, shut off the breaker/disconnect for 5 minutes, then restore power
When to call a technician
The check-run procedure has to be re-initialized by the installer at the outdoor unit and branch boxes. If this is a new install, call the installing contractor back - the system was never commissioned.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25
- Check-run Unfinished - Fujitsu General Help Center (Fujitsu General America, Inc., RLF / RLF1 multi-zone indoor units, AOU48RLXFZ / AOU48RLXFZ1) · checked 2026-08-25
Code 18: External communication error
External communication error. After receiving a signal from the external I/O PCB, the indoor controller has not received the same signal again for 15 seconds.
Manual wording: “External Communication Error - After receiving a signal from the external I/O PCB, the same signal has not been received for 15 seconds.”
Documented for: RGLX, RL2/RLS3/RLB/RLXB wall mounted, RLF/RLF1 multi-zone
Likely causes, most common first
- Loose or removed connection between the controller PCB and the external I/O PCB
- Open cable or mis-wiring on the external I/O PCB
- Failed controller PCB
What you can safely check yourself
- Turn the power off at the breaker for about 5 minutes and back on to see whether the code clears
When to call a technician
This fault lives entirely on the accessory I/O board and its harness inside the unit. A technician must open the electrical box to inspect it.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25