Error keeps coming back after every reset: corroded wire connection
The CH05 came and went. A power cycle cleared it some days, not others. A previous contractor quoted an outdoor control board replacement at $350. But an error that clears on restart is usually a connection that drops, not a board that has failed.
By Team Snowflake | Reviewed 24 Mar 2026
Case summary
LG Wall-mounted10 years oldHDBAng Mo Kio, Singapore
- Concern
- A previous contractor advised replacing the outdoor control board at $350.
- Previous advice
- Previous contractor said outdoor control board needed replacing at $350
- Found
- Corroded signal connection at outdoor unit causing intermittent communication loss
- Key check
- Checked the outdoor wire connector and found green corrosion. The connection was much weaker than it should be.
- Result
- CH05 cleared the moment the new connector was refitted, and the signal held steady. The unit has run without the error returning, at a fraction of the quoted control board replacement cost. The owner avoided a $350 part that was never the fault.
What we were told
The aircon kept showing an error code. Switching it off and on sometimes cleared it, but lately the code returned within hours. The owner had grown tired of resetting it. A previous contractor had quoted an outdoor unit board replacement at $350, so the owner wanted a second opinion before spending.
What we checked
CH05 is a communication fault between the indoor and outdoor units. Because it cleared on a restart and kept returning, a dropping connection was more likely than a dead board. We started at the wiring before touching any components, since that is the cheaper fault to rule out.
The CH05 error was present on arrival. The indoor unit showed the fault and would not start.
The communication wire tested fine end to end, with no breaks along its length. So the cable itself was not the problem.
The outdoor connection point had visible green corrosion on the communication wire connector.
The corroded connector held the wire far more loosely than a sound one should, which is enough to interrupt the signal.
No other wire connections showed corrosion or looseness, so the fault was contained to this one point.
What we found
The communication cable connector at the outdoor unit had corroded over the years. Moisture worked into the connection and ate away at the contact, weakening the signal between the indoor and outdoor units. When the contact dropped out, CH05 appeared. A restart sometimes nudged the contact back together and restored the signal for a while, which is why the fault came and went rather than staying on.
What fixed it
We cleaned the corroded connection, stripped the cable back to fresh copper, and fitted a new connector for a solid contact. We applied protective grease over the joint to slow future corrosion in the damp outdoor air. No control board replacement was needed. We advised checking the outdoor connections during future servicing, since the same exposure can corrode them again over time.
Outcome
CH05 cleared the moment the new connector was refitted, and the signal held steady. The unit has run without the error returning, at a fraction of the quoted control board replacement cost. The owner avoided a $350 part that was never the fault.
What this case teaches us
An error that clears on restart points to a loose contact, not a dead board
- CH05 means the indoor and outdoor units have lost their signal. A corroded or loose connector breaks that signal as easily as a failed board does, and costs far less to fix.
- When a power cycle clears the fault for a while, the part is not dead. It is dropping in and out. That pattern points to a connection, so the wiring deserves a look before any board is quoted.
- Outdoor connectors sit in heat and humidity for years. A simple corrosion check during servicing catches this fault early, before the error starts returning.
Related reading
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