Pre-war shophouse error: signal wire chafed in trunking

A pre-war shophouse unit near Kallang threw an error code with no clear pattern, running fine some days and faulting within an hour on others. Signal wiring from a later rewiring, routed through a tight bend in old masonry, can hide a chafe point that mimics a control board fault.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Panasonic Wall-mounted15 years oldShophouseKallang, Singapore

Concern: The tenant feared a failing control board, priced closer to a full unit replacement than a repair.
Found: Signal wire chafed through inside old trunking, causing an intermittent connection
Key check: Traced the signal wire's full run through the trunking added during a past rewiring instead of replacing the control board first
Result: The unit ran fault-free through several weeks of normal use afterward. The tenant avoided paying for a control board that was never the actual problem.

What we were told

The unit faulted at random times, sometimes within the first hour of running and other times not for a full day. There was no link to weather, time of day, or how hard the unit was working. A previous visit had already reset the error once, and it returned within a week. The trunking along the ceiling had not been opened in years.

What we checked

The lack of any pattern was itself the strongest clue, so the board stayed in place on the first visit. A control board fault usually shows some consistency; a wiring fault that depends on vibration, flex, or a sharp edge inside old trunking tends to look genuinely random.

The control board's diagnostic self-test passed cleanly when powered on the bench.
The signal wire's insulation had worn through at one point where the trunking narrowed.
The exposed conductor made intermittent contact with the trunking edge, consistent with the random fault pattern.
No other component in the outdoor or indoor unit showed a fault when tested independently.

What we found

The signal wire ran through a section of trunking added during a past rewiring, routed through a tight bend in the shophouse's original masonry where the channel narrowed slightly. Over time, vibration wore through the wire's insulation at that exact point, letting the bare conductor touch the trunking edge intermittently. Contact happened only when the wire sat at a particular angle, which explains why the fault never followed a clean schedule.

What fixed it

We replaced the damaged section of signal wire and rerouted it clear of the narrowed point in the trunking. We did not replace the control board, since it tested correctly on its own. We advised checking the full trunking run again at the next service, since the building's age means other sections could wear through the same way over time.

Outcome

The unit ran fault-free through several weeks of normal use afterward. The tenant avoided paying for a control board that was never the actual problem.

What this case teaches us

A random, patternless error often points to a wire, not the board

An error that appears with no link to weather, runtime, or time of day is more likely a loose or damaged wire than a failing board.
Old trunking can hide a chafe point that only faults when the wire flexes or vibrates against a sharp edge.
Ask for the signal wire to be traced along its full run before approving control board replacement in an older shophouse.

Questions this case answers

Why does my aircon throw an error at random with no pattern?

A fault ignoring weather, runtime and time of day usually sits in the wiring rather than the board. In this pre-war Kallang shophouse the unit faulted within an hour on some days and not at all on others. That randomness matched a wire making intermittent contact, not a board failing in a consistent way.

What can chafe a signal wire inside old trunking?

A narrow point where the channel pinches the cable. The signal wire here ran through trunking added during a past rewiring, forced around a tight bend in the shophouse's original masonry. Vibration wore the insulation through at that spot, leaving bare conductor touching the trunking edge whenever the wire sat at a particular angle.

Aircon error returns after being cleared: what does that indicate?

That the underlying condition is still present. Clearing a code removes the report, never the cause. On this unit the control board's diagnostic self-test passed cleanly on the bench and nothing in either the indoor or outdoor unit showed a fault, which left the damaged wire run as the only thing capable of producing the pattern.

What should be traced before a control board is replaced?

The signal wire along its full run, particularly in an older building where trunking has been added over the years. Replacing the damaged section and rerouting it clear of the narrowed point ended the fault here, and the board stayed in place. The trap is buying an expensive part that has already tested correctly.

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