Error Keeps Coming Back After Every Reset: Corroded Wire Connection

• •Concern: Previous advice was outdoor PCB replacement at $350
• •Previous advice: Previous contractor said outdoor PCB needed replacing at $350
• •Key check: Terminal inspection revealed green oxidation on communication cable crimp. Contact resistance measured 12 ohms vs expected near-zero

An intermittent communication error that clears on power cycle pointed to a connection issue rather than a board failure. We started at the wiring before touching any components.

• •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 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.

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, and the unit has been running without error recurrence. At a fraction of the quoted PCB replacement cost.

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. That makes 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.