Daikin aircon U3 error code
Use this Daikin U3 error code guide to decide when to stop resetting, what to capture, and what to check before parts are quoted.
What does Daikin U3 mean?
Daikin U3 is listed as check operation not executed or transmission error in Ceiling Cassette, Ceiling Suspended, Fan Coil rows such as Fan Coil, General RA self-diagnosis guide. The loaded row is source-backed by official diagnostic material. Confirm the exact model, series, or signal row before accepting a parts quote.
Loose, corroded, crossed, or damaged indoor-outdoor signal wiring.
Terminal block, connector, or junction fault on the indoor or outdoor side.
Indoor or outdoor PCB communication circuit fault after wiring is proven sound.
What to do now
Use these steps before another reset, signal-wire check, or PCB quote.
Stop using the unit if U3 returns
If U3 returns after one reset, stop repeated restarts and get the matching source row diagnosed.
Reset U3 once
Capture the U3 display first, then power-cycle once only and note whether the same fault returns.
Send these to us
U3 error code, a clear display photo, Daikin model stickers, affected rooms, reset result, and whether one room or every room failed
Source-specific guidance
These diagnostic-reference notes help match the code to the exact model. Electrical, refrigerant, wiring, resistance, and component checks are technician work, not DIY steps.
| Source detail | What it says |
|---|---|
| Source repair action | Stop the system if it smells burnt, leaks, or trips power; note the exact model and code before booking diagnosis. |
| Singapore / model note | Official Daikin SM-TS3 self-diagnosis row. Manual causes: Check operation is not executed. |
What to check before repair
Use this split to separate safe evidence capture from the tests a technician should prove before quoting parts.
| You can check | Technician should confirm |
|---|---|
| Before resetting U3, take a clear display photo. | Match U3 against the exact model-family source row before quoting parts. |
| Capture the Daikin indoor and outdoor model stickers so the correct family row is used. | Test communication terminals, cable continuity, polarity, and outdoor power. |
| Note whether one room, several rooms, or the whole system is affected, plus whether it returns after one reset. | Read indoor and outdoor PCB indicators only after the signal path is proven sound. |
What changes the next step
These clues decide whether the first check is room-side, shared outdoor-side, refrigerant-side, source-table, or model-family confirmation.
| What you see | What it points to |
|---|---|
| Only one indoor unit shows U3. | The affected room, indoor board path, wiring route, or local component should be checked first. |
| Several rooms or the outdoor unit show the same U3 fault. | The shared outdoor side, power path, communication trunk, or refrigerant circuit needs priority checking. |
| The fault returns immediately after one reset. | Start with the source-row diagnostic branch before approving parts. |
| The model family is different from the row you found online. | Use the model or series filter first; same-looking codes can still belong to different diagnostic tables. |
| The model belongs to Ceiling Cassette, Ceiling Suspended, Fan Coil rows such as Fan Coil, General RA self-diagnosis guide. | The loaded row is source-backed by official diagnostic material. Use the matching source row before quoting parts. |
Wiring or PCB decision
Daikin U3 should start with terminal, signal-cable, and power checks. PCB replacement only makes sense after the communication path is proven sound.
A loose terminal or bad junction is a targeted repair once the path is confirmed.
Signal-wire replacement depends mostly on access through trunking, ceiling, or concealed routes.
PCB cost should be weighed against age only after wiring and power checks pass.
Daikin U3 questions
What does the Daikin U3 error mean?
Can I fix a Daikin U3 error myself?
Is it safe to keep running the aircon with a U3 error?
What causes a Daikin U3 error?
Will a Daikin U3 error need a repair or a full replacement?
What should I send a technician about a Daikin U3 error?
Confirm the fault
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Read next
Use these if the quote mentions the parts, checks, or repair path this code points to.