What is a PCB swap test?

A PCB swap test moves the suspected faulty board from one indoor unit to another in the same system. If the error follows the board, the board is confirmed faulty. If the error stays in the original location, the fault is in the wiring or another component at that unit.

Why did only one unit show E1 if they share the same outdoor unit?

Each indoor unit has its own PCB that handles communication with the outdoor unit independently. A failure in one indoor board does not affect the others — they continue communicating normally through their own boards.

Is it worth repairing the indoor PCB instead of replacing it?

Board-level repair is possible in some cases, but communication relay failures are difficult to repair reliably. A replacement board is typically more cost-effective and comes with a parts warranty, making it the more practical option.

Samsung E1 Indoor PCB Communication Relay Failure

Aircon case in Sengkang, Singapore: electrical/control traced to indoor unit PCB communication relay failure after targeted diagnosis checks.

Case Details

Reported: One of my three aircon units keeps showing an error code. The other two are working fine. It has been like this for about a week. I am not sure if it is a wiring problem or something inside the unit.
Unit: Samsung · Wall-mounted · 7–12 years
Location: Condo · Sengkang, Singapore

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 unit model. We also noted that at seven-plus years, the other indoor PCBs could eventually develop similar issues, but there was no reason to preemptively replace boards that were still functioning normally.

The replacement indoor PCB was installed and E1 cleared immediately. All three units are now operating normally. The swap test avoided 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 provides definitive confirmation before any parts are purchased.

Same situation with your aircon?

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