Daikin VRV Error Code UA

Full Diagnosis

UA fires when the outdoor unit's PCB detects a system configuration that doesn't match its supported combination rules — most commonly too many indoor units connected for that outdoor module's rated capacity, a mismatch between the refrigerant type set on indoor versus outdoor units, or missing setup after an outdoor PCB replacement. Because VRV outdoor modules support a much larger, more complex mix of indoor unit types and connected capacity than a single-zone SkyAir unit, combination errors are more likely here and require checking total connected capacity ratio against the outdoor unit's allowable range. The whole outdoor module — and all indoor units branched from it — is prevented from starting until the mismatch is corrected. Distinguish from AJ (an individual indoor unit's own capacity-setting adaptor issue) — UA is a system-wide combination/configuration check performed at the outdoor unit level.

All Recorded Causes

Total connected indoor unit capacity exceeds the outdoor unit's allowable range, mismatch between the refrigerant type (e.g., R-410A vs R-32) configured on indoor versus outdoor units, outdoor unit PCB field settings not re-entered after replacing to a spare PCB, incompatible indoor unit model connected to that outdoor system, defective outdoor unit PCB.

Verify Before Replacing Parts

1. Confirm the exact Daikin model family and vrv context before acting on a generic code description.
2. Verify airflow first, then confirm operating pressures and temperature relationship before adjusting charge, since total connected indoor unit capacity exceeds the outdoor unit's allowable range, mismatch….
3. Look for restrictions, iced coils, or dirty heat-transfer surfaces that can mimic a charge problem, and separately confirm the next candidate on the list.
4. After the correction, run the system long enough to confirm the vrv fault does not return under normal load.