Aircon Flashing Light After Renovation

Case Details

What We Checked

• Fault onset matched the renovation date exactly — no prior history of errors on this unit. Service records showed zero stored error codes before that week.
• Signal wire terminal near the trunking section was loose. It had shifted about one millimetre from the screw connector — enough to break electrical contact under slight movement.
• Wire made intermittent contact — enough to communicate sometimes but not reliably under vibration or thermal movement. Tapping the trunking near the terminal reproduced the flashing error on demand. This confirmed the connection was marginal.
• Both indoor and outdoor PCBs tested normal with no stored fault codes. The boards were undamaged despite the intermittent communication dropouts.
• Voltage at the signal wire terminal fluctuated when the connector was disturbed. It dropped below the communication threshold momentarily before recovering — matching the intermittent pattern the client described.

The Diagnosis

The signal wire that carries communication between the indoor and outdoor units runs through PVC trunking along the bedroom wall. During renovation, workers moved and reseated the trunking section to access the wall behind it. The signal wire terminal at the connector block was pulled slightly in the process. The shift was not enough to disconnect it visibly, but enough to unseat it by about one millimetre. At that depth, the wire made contact most of the time. But any slight movement from thermal expansion or compressor vibration was enough to break the connection. When communication dropped, both boards flagged a fault and the indoor unit flashed its error light. When the wire settled back into contact, communication resumed and the unit appeared to recover — until the next disruption. The boards were never damaged. The fault was purely mechanical at the terminal.

What Fixed It

We reseated the signal wire terminal fully into the screw connector and tightened it to proper torque. We also inspected the rest of the wire run through the trunking section moved during renovation — no other terminals were disturbed. We then ran the unit through a full start-and-cool cycle, monitoring for communication dropouts. The system held stable with no flashing and no error codes stored on either board. No PCB replacement was needed on either unit. We recommended the client inform the renovation contractor so future trunking work could be handled with more care around the wire path.

The flashing stopped and cooling held steady through the afternoon. No parts were replaced — the boards and wiring were all original.

Why This Happens

When a flashing error starts right after nearby work.

• Board failures develop over time from age, heat, or power surges. They leave a trail of stored error codes and measurable wear. A fault that appears the same day as nearby renovation work with no prior error history is almost never the board. It is nearly always a physical disturbance to the wiring path.
• Signal wires run through trunking along walls and ceilings. Any work that moves, bumps, or reseats trunking can loosen a terminal or shift a connector just enough to break communication. Even one millimetre of shift at a screw terminal can drop contact pressure below the threshold for reliable signal transmission.
• Matching the fault onset to the renovation timeline is the fastest diagnostic step. It narrows the search to a specific wire section before any parts are tested or boards are condemned. A simple question — when exactly did the flashing start? — often points directly to the cause.
• A partially unseated terminal can look normal on visual inspection. The wire is still in the screw terminal, but one millimetre of movement is enough to break contact under thermal expansion or vibration. The technician needs to tug-test each terminal and measure signal voltage stability, not just look at the connections.