R-Pro › Field cases › Air conditioning
Comm Line L/N Swapped — #1 Cause of Communication Faults
Likely causes
Comm line carries both 220V power AND data (outdoor→indoor)
Check: Korean AC comm lines = 2 wires of a 4-pin (or 14/4 stranded) cable carry both 220V power and VDC pulse signal from outdoor→indoor. **L/N swapped** = indoor PCB comm IC can't read signal → comm fault (LG CH05, Samsung E102). Check L-N = 220V with multimeter and verify phase. Standard: L = red/brown, N = blue/black. But colors vary by installer.
What to do: **L/N swapped fix**: at both outdoor and indoor terminal blocks, exchange L and N wire positions. Keep both ends same direction. After rewire = power ON → wait 3–4 min comm → error code clears. **Moisture/open**: replace with new 14/4 stranded. Outdoor-exposed sections = waterproof tape + cable sleeve. **Leakage**: megger insulation; <1 MΩ = replace immediately.
**Field stats**: 30%+ of comm-error visits are L/N swap. Common right after new install on first run. **At install**: photograph both terminal blocks, verify color match. Korean embedded conduits = comm line replacement is huge work (wall break needed) — verify thoroughly at install. Chinese cables often leak within 5 years; use KS/UL-certified.
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