Can a corroded terminal really cause a communication error?

Yes. Communication signals between indoor and outdoor units travel through low-voltage wiring. Even a small increase in resistance from corrosion can degrade or block the signal, triggering error codes like CH05.

Why did the error clear sometimes after a power cycle?

Thermal expansion and contraction can temporarily shift a corroded contact point just enough to restore the connection. This is why intermittent errors that clear on restart often point to wiring rather than a failed board.

Should I replace the outdoor PCB if CH05 keeps appearing?

Not necessarily. CH05 indicates a communication fault, which can be caused by wiring issues, terminal corrosion, or a board failure. A proper diagnosis should check wiring and terminals first before concluding the PCB needs replacement.

LG CH05 Communication Error From Corroded Wiring Terminal

Aircon case in Ang Mo Kio, Singapore: electrical/control traced to corroded signal terminal at outdoor unit causing intermittent communication loss after targeted diagnosis checks.

Case Details

Reported: The aircon keeps showing an error code. Sometimes it clears if I switch it off and on, but lately it comes back within hours. My previous contractor said the outdoor unit board needs replacing — that was quoted at $350.
Unit: LG · Wall-mounted · 7–12 years
Location: HDB · Ang Mo Kio, Singapore

What We Checked

CH05 error was present on arrival — indoor unit displayed the fault and would not start.
Communication cable continuity tested fine end-to-end with no open circuits.
Outdoor unit terminal strip showed visible green oxidation on the communication wire crimp.
Contact resistance at the corroded terminal measured 12 ohms — far above the expected near-zero reading.
No other terminals showed signs of corrosion or looseness.

The Diagnosis

The communication cable crimp at the outdoor unit terminal strip had corroded over the years. Moisture from condensation built up around the terminal, causing oxidation that increased contact resistance. When resistance was high enough, the signal between indoor and outdoor units dropped out and triggered CH05. Power cycling sometimes temporarily restored enough contact to clear the error, which explained the intermittent pattern.

What Fixed It

We cleaned the corroded terminal, stripped back the cable to fresh copper, and re-crimped with a new terminal lug. We also applied protective grease to prevent future oxidation. No PCB replacement was needed. We recommended checking the terminal strip during future servicing visits, as the outdoor unit's age makes it susceptible to further corrosion over time.

CH05 cleared immediately after the terminal was re-crimped. The unit has been running without error recurrence. The repair cost a fraction of the quoted PCB replacement.

Why This Happens

Why intermittent error codes often point to wiring, not boards.

An error that clears after a power cycle and returns later is a hallmark of a loose or corroded connection — not a failed component.
Outdoor unit terminal strips are exposed to humidity and condensation, making them a common corrosion point on units older than five years.
Measuring contact resistance at each terminal is a quick check that can save hundreds in unnecessary PCB replacements.

Same situation with your aircon?

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