Daikin Split & Multi-Split Error Code U7

Full Diagnosis

U7 signals a transmission failure between multiple outdoor units (on systems with an outdoor storage/booster unit or linked outdoor modules) or between the outdoor unit and an external control adaptor, rather than between indoor and outdoor equipment. This affects the whole system tied to the failed communication link, since outdoor-to-outdoor coordination governs shared compressor and defrost sequencing. U7 differs from U4 (indoor-outdoor transmission, which isolates faster and is far more common on standard single-outdoor-unit residential splits) and from U5 (indoor unit-to-remote-controller only) — U7 specifically points to wiring or hardware between outdoor-side components.

All Recorded Causes

Broken, disconnected, or miswired transmission cable between outdoor units. Faulty connection between the outdoor unit and its external control adaptor. Incorrect outdoor unit address or DIP switch setting on a linked system. Corroded or loose terminal connections at the outdoor transmission terminal block. Electrical noise on the outdoor transmission wiring run. Defective outdoor unit PCB transmission circuit.

Verify Before Replacing Parts

1. Confirm the exact Daikin model family and split/ multi split context before acting on a generic code description.
2. Confirm board LEDs, wiring polarity, and model compatibility before replacing control boards — this Daikin fault points at broken, disconnected, or miswired transmission cable between outdoor units.
3. Check for intermittent communication faults caused by connectors, moisture, or damaged harnesses, and rule out faulty connection between the outdoor unit and its external control adaptor.
4. After the correction, run the system long enough to confirm the split/ multi split fault does not return under normal load.