Daikin SkyAir Error Code UA

Full Diagnosis

UA reports an improper combination of indoor and outdoor units — a mismatch condition detected at startup where the connected indoor unit capacity, quantity, or refrigerant type is incompatible with the outdoor unit's programmed configuration. This differs from U4's communication wiring fault and from MC's centralized-control address duplication in that UA is a configuration/compatibility check failure rather than a wiring or addressing problem; it commonly appears after a PCB replacement where field setting was skipped, or when a unit exceeding the rated indoor connection count is added.

All Recorded Causes

Number of connected indoor units exceeds the outdoor unit's rated capacity, defective outdoor unit PCB, mismatch between the refrigerant type configured on indoor versus outdoor units, outdoor unit PCB field setting not performed after replacing it with a spare/replacement PCB, incorrect model or capacity code entered during commissioning.

Verify Before Replacing Parts

1. Confirm the exact Daikin model family and skyair 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 number of connected indoor units exceeds the outdoor unit's rated capacity, defective outd….
3. Check for intermittent communication faults caused by connectors, moisture, or damaged harnesses, and rule out the next candidate on the list.
4. After the correction, run the system long enough to confirm the skyair fault does not return under normal load.