Daikin Chiller

Daikin Chiller Error Code U3

Troubleshooting guide for the Daikin Chiller system fault U3.

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What It Means

Indicates that the initial check (test run) operation required after installation or a control reset has not been completed, so the chiller control holds startup in a safe, non-running state — this is a commissioning-status flag rather than an active hardware fault.

Possible Causes

  • Check/test run procedure never performed after installation or after a controller replacement.
  • Check operation aborted partway through.
  • DIP switch or field setting left in test mode.
  • Address or wiring verification left incomplete.
  • Control PCB replaced without re-running startup commissioning.

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

Indicates that the initial check (test run) operation required after installation or a control reset has not been completed, so the chiller control holds startup in a safe, non-running state — this is a commissioning-status flag rather than an active hardware fault. It differs from U4, U6, and U8, which all report an ongoing communication breakdown on a specific wiring segment (outdoor-to-indoor, indoor-to-indoor, or between remote controllers) rather than an incomplete commissioning step. Running the manufacturer's check/test operation from the controller typically clears this code once wiring and addressing are confirmed correct.

All Recorded Causes

Check/test run procedure never performed after installation or after a controller replacement. Check operation aborted partway through. DIP switch or field setting left in test mode. Address or wiring verification left incomplete. Control PCB replaced without re-running startup commissioning.

Verify Before Replacing Parts

  1. Confirm the exact Daikin model family and chiller 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 check/test run procedure never performed after installation or after a controller replacem….
  3. Check for intermittent communication faults caused by connectors, moisture, or damaged harnesses, and rule out check operation aborted partway through.
  4. After the correction, run the system long enough to confirm the chiller fault does not return under normal load.

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