Error returns after every reset: corroded wire connection

The CH05 came and went, cleared by a power cycle some days and not others. The outdoor control board was the obvious thing to suspect. But an error that clears on restart is usually a connection that drops, not a board that has failed.

By Team Snowflake | Updated 28 Jul 2026

Case summary

LG Wall-mounted7-12 years oldHDBAng Mo Kio, Singapore

Concern: The worry was that the outdoor control board needed replacing outright.
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 connection was remade at the one point that had been dropping out, and the unit has run since without the error returning. No board was replaced.

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. An outdoor board replacement was where this seemed to be heading, 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 connection was remade at the one point that had been dropping out, and the unit has run since without the error returning. No board was replaced.

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.

Questions this case answers

Why does an LG CH05 error clear when the aircon is switched off and on?

Because the part is dropping in and out rather than sitting dead. A restart can nudge a weak contact back together and hold the signal for a while. On this Ang Mo Kio unit the connector at the outdoor end had corroded and gripped the wire far more loosely than a sound one should.

Is CH05 always a control board problem?

No. The code only says the indoor and outdoor units have lost their signal. A corroded or loose connector breaks that link just as effectively as a failed board does, and it costs far less to put right. Here the cable tested fine end to end, and the fault sat at one connection point outdoors.

What causes green crust on the aircon wires outside?

Moisture working into the connection over the years. Outdoor terminals sit in heat and humidity with no shelter, and the contact surface slowly oxidises. That green build-up is the visible part of it. It weakens the joint until the signal starts dropping, which is what drove the repeat errors on this unit.

How do I stop outdoor wire connections corroding again?

Strip back to fresh copper, fit a sound connector, and cover the joint with protective grease, which is what we did here. Then have those outdoor connections looked at during servicing rather than only when something faults. The same exposure will work on them again, so catching oxidation early is what stops a repeat.

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