One Unit Showing Error, Others Fine: Indoor Board Relay Confirmed Dead
Aircon case in Sengkang, Singapore: electrical/control traced to indoor unit PCB communication relay failure after targeted diagnosis checks.
Case Details
| Unit | SamsungWall-mounted |
|---|---|
| Age | 10 years old |
| Location | CondoSengkang, Singapore |
| Reported | One of three aircon units had been showing an error code for about a week while the other two worked fine. The question was whether it was a wiring problem or something inside the unit. |
What We Checked
- E1 error was constant on the bedroom unit — it would not start.
- The other two indoor units operated normally with no errors.
- Communication cable between the faulted indoor unit and the outdoor unit tested intact with correct continuity.
- Terminal connections at both ends were clean with no corrosion.
- PCB swap test: moved the bedroom unit PCB to the living room unit. E1 followed the board to the living room, and the bedroom unit worked with the living room board.
The Diagnosis
The indoor unit PCB communication relay had failed. This relay handles the signal exchange between the indoor board and the outdoor unit. When it fails, the indoor unit can no longer communicate, triggering E1. The swap test confirmed the fault was on the board itself — moving it to a different unit reproduced the error in the new location while the original unit resumed working with a functional board.
What Fixed It
We recommended replacing the indoor PCB for the affected unit. The wiring, outdoor unit, and other indoor units were all confirmed working. We sourced the correct replacement board for the model. At seven-plus years, the other indoor PCBs could eventually develop similar issues, but there was no reason to preemptively replace boards still working normally.
The replacement indoor PCB was installed and E1 cleared immediately — all three units are now operating normally, with the swap test having eliminated any guesswork in the diagnosis.
Why This Happens
How a PCB swap test isolates the faulty board without guesswork.
- In a multi-split system where only one unit faults, the fault is almost certainly in that specific indoor unit — not the shared outdoor unit or wiring.
- A PCB swap test moves the suspected board to a different indoor unit. If the error follows the board, the diagnosis is confirmed. If it stays, the fault is elsewhere.
- This test avoids ordering a replacement board on assumption. It gives definitive confirmation before any parts are purchased.
Related Reading
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