HVACopediaFujitsu · Heat pump
Outdoor LED2 1 flash Serial comms error, outdoor to indoor unit B (outdoor board LED)
What the control is telling you
Multi-zone 18/24 outdoor board: LED2 flashes 1 time while the other LEDs stay off. Same fault family as indoor code 11. The LEDs sit on the back side of the board and are seen through a hole.
Applies to: Fujitsu 18 type (2-zone) and 24 type (3-zone) multi outdoor units
Likely causes
- Loose, wrong or broken wire on terminals 1-2-3
- Supply voltage out of range
- Electrical noise / poor ground
- Indoor or outdoor main PCB failure
- Outdoor or indoor fan motor dragging down the circuit
Test and repair steps
- Look at the outdoor PCB LEDs (rear of the board, viewed through the hole) and count the flashes on each LED.
- Then follow the checks for indoor code 11: Reset power and run; if it does not return, check for outside causes (ground, noise sources near the cable).
- Check the 1-2-3 connection cable at both units for loose screws, swapped wires or damage; correct per the install manual.
- Check supply voltage at the outdoor terminal block (NA units: 208/230 V, keep within 187-253 V).
Settings for these units
Operating range and service space · Fujitsu multi-zone outdoor 18/24 type
| Item | Value |
|---|---|
| Cooling outdoor range | 14 to 115 F DB |
| Heating outdoor range | 5 to 75 F DB |
| Cooling indoor range | 65 to 90 F DB |
| Heating indoor range | 60 to 88 F DB |
| Rear (open top, rear wall only) | 4 in. or more |
| Rear + sides | 4 in. rear, 10 in. sides |
| Front wall only | 24 in. or more |
| Between side-by-side units | 10 in. or more |
| Base height | 2 in. or more above floor |
Unit tilt no more than 3 degrees and never toward the compressor side.
Below 32 F outdoor do not fit the drain pipe/caps (freezing).
Other codes on the same units
- Outdoor LED1 6 flashes 3-way valve sensor error, unit A (outdoor board LED)
- Outdoor LED1 7 flashes Compressor temperature sensor error (outdoor board LED)
- Outdoor LED1 8 flashes Heat sink temperature sensor error (outdoor board LED)
- Outdoor LED1 9 flashes High pressure switch 1 error (outdoor board LED)
- Outdoor LED2 5 flashes 2-way valve sensor error, unit B (outdoor board LED)
- Outdoor LED2 6 flashes 3-way valve sensor error, unit B (outdoor board LED)
- Outdoor LED3 1 flash Serial comms error, outdoor to indoor unit C (24 type) (outdoor board LED)
- Outdoor LED3 5 flashes 2-way valve sensor error, unit C (24 type) (outdoor board LED)
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Source: Fujitsu Outdoor unit 18-24 type (North American trilingual) installation P-N 9374747160.pdf - section 8.2 Outdoor unit LED. Summarized in our own words; check the original manual for your model.
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