What It Means
Malfunction of transmission (other system).
Daikin SkyAir
Daikin SkyAir Error Code U9
Troubleshooting guide for the Daikin SkyAir system fault U9.
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Possible Causes
- Transmission error between other indoor and outdoor units Defective electronic expansion valve of other indoor unit Defective indoor unit PCB of other indoor unit.
- Improper connection of transmission wiring between indoor and outdoor unit.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Malfunction of transmission (other system)
All Recorded Causes
Transmission error between other indoor and outdoor units Defective electronic expansion valve of other indoor unit Defective indoor unit PCB of other indoor unit Improper connection of transmission wiring between indoor and outdoor unit
Verify Before Replacing Parts
- Confirm the exact Daikin model family and skyair context before acting on a generic code description.
- Start with line voltage, low voltage, and board output checks in sequence so the fault is isolated cleanly — the data plate flags transmission error between other indoor and outdoor units Defective electronic expansion v….
- Inspect connectors, relay outputs, and any recently replaced electrical parts for mismatch or loose fit, and verify improper connection of transmission wiring between indoor and outdoor unit.
- After the correction, run the system long enough to confirm the skyair fault does not return under normal load.
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