Ceiling unit random shutdowns traced to loose terminal after renovation

What we found

The on-and-off pattern and the renovation timing pointed toward a connection fault, not a board-level failure. A PCB fault would typically produce steady behaviour or an error code.

• No stored error code on the unit. It reset cleanly after each shutdown.
• Voltage supply to the unit was stable at the isolator.
• Terminal block at the indoor unit had a connection with visible looseness.
• Gently tapping the loose terminal reproduced the dropout during testing.

The terminal block at the indoor unit had loosened during nearby renovation work. The shaking from construction passed through the ceiling. Under normal use the link held most of the time. But now and then, shaking or heat shift caused brief power loss. This made the unit shut down and restart.

What we did

The PCB is not damaged. The terminal block link needs to be tightened and tested under load. Once the link is firm, the shutdowns should stop. No board swap is needed.

After the terminal was re-secured and tested under load with induced vibration, the unit ran without dropout. The random shutdowns did not return. No PCB was replaced.

What we learned

Why renovation shaking can cause on-and-off aircon shutdowns.

• A loose terminal creates on-and-off contact. The unit runs fine when the connection holds. It drops out when vibration or heat expansion breaks the contact briefly.
• Checking all terminal links at the indoor unit is a quick first step. This can rule out wiring faults before any PCB testing begins.
• Construction shaking can loosen terminal block links at the indoor unit. This happens even if the renovation did not directly touch the aircon system.