Daikin Fan Coil

Daikin Fan Coil Error Code U1

Troubleshooting guide for the Daikin Fan Coil system fault U1.

ACLogics Standardize Fan Coil diagnostics See the commercial workflow → Standardize Fan Coil diagnostics

What It Means

Reverse phase, open phase.

Possible Causes

  • Power supply reverse phase.
  • T phase open phase.
  • Defective outdoor unit PCB (A1P).

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.
New to this code? Click to see why this happens

Full Diagnosis

Reverse phase, open phase

All Recorded Causes

Power supply reverse phase T phase open phase Defective outdoor unit PCB (A1P)

Verify Before Replacing Parts

  1. Confirm the exact Daikin model family and fan coil context before acting on a generic code description.
  2. Confirm filter condition, blower operation, and coil cleanliness before replacing any controls — start by ruling out whether power supply reverse phase.
  3. Measure airflow-related readings that match the symptom, such as temperature split or static pressure, and check whether t phase open phase.
  4. After the correction, run the system long enough to confirm the fan coil fault does not return under normal load.

Diagnosing Fan Coil across a fleet?

ACLogics standardizes commercial Fan Coil diagnostics across your whole team — consistent steps, less guesswork on every call.

See the commercial workflow →