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P/Q Communication Wire Open/Short Circuit — Indoor Unit Communication Error

Likely causes

P/Q wiring connector poor connection or terminal under-torque

Check: Check torque of each P/Q terminal block connection: normal 0.5–0.8 N·m → visually inspect terminals for oxidation/corrosion

What to do: Sand oxidized terminals and reattach → re-tighten to specified torque (0.5–0.8 N·m) → clear communication error codes and restart

Termination resistor not installed — frequent errors from signal reflection

Check: Measure resistance between P-Q at the farthest indoor unit terminal block: normal 120Ω — verify termination resistor installation

What to do: Install 120Ω termination resistor at P-Q terminals of the farthest indoor unit → re-check communication error frequency

P/Q wiring total length exceeds 500m — signal attenuation

Check: Calculate total P/Q wiring length → check if exceeds 500m → measure P-Q voltage at farthest indoor unit (normal DC 14–16V)

What to do: Install additional repeater → review wiring route to reduce total length → consider adding outdoor unit or splitting the system

Field tip

Checking P/Q terminal resistance of 120Ω is essential at first on-site diagnosis — the most common cause of intermittent communication errors when not installed.

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