Daikin Air conditioner C4 error
C4 is listed in Daikin's official, model-scoped air-conditioner fault table as heat-exchanger temperature sensor fault.
Reference source listed as Daikin official FTX25KMV1B / FTX35KMV1B operation manual 3P393186-11R.
Open official source ↗heat-exchanger temperature sensor fault
Stop if there is smoke, a burning smell, damaged wiring, repeated breaker operation, or refrigerant leakage. Do not bridge or electrically probe the sensor circuit. Record the code, switch the air conditioner off, and contact the Daikin service shop; the manual says not to repair, dismantle, reinstall, or modify the unit yourself.
Typical symptoms
Fault area and what the code does not prove
Separate the manufacturer-defined condition from components that still need exact-model diagnosis.
Safe next steps
- 1Confirm the exact Daikin Air conditioner C4 model and displayed code before taking action.
- 2Keep the appliance in a safe state and use only the external checks named in the official source.
- 3If the condition remains, stop and arrange qualified service; do not open panels or bypass a safety device.
Step-by-step diagnosis
- 1Photograph the complete C4 display before changing controls or removing power
- 2Confirm that the full model number is covered by this scope: Daikin room air-conditioner models FTX25KMV1B and FTX35KMV1B
- 3Confirm that the observed condition matches the published meaning: heat-exchanger temperature sensor fault
- 4Published check — Do not bridge or electrically probe the sensor circuit
- 5Published check — Record the code, switch the air conditioner off, and contact the Daikin service shop
- 6Published check — the manual says not to repair, dismantle, reinstall, or modify the unit yourself
- 7Stop at the published service boundary after these actions
- 8do not add a restart or test cycle that Daikin does not specify for C4
- 9Published check — Give service the C4 photo, full model and serial number, when it appeared, and the result of every published external check
- 10Stop at the published service boundary after these actions; do not add a restart or test cycle that Daikin does not specify for C4
Service-safe actions
- 1Do not bridge or electrically probe the sensor circuit
- 2Record the code, switch the air conditioner off, and contact the Daikin service shop
- 3the manual says not to repair, dismantle, reinstall, or modify the unit yourself
- 4Give service the C4 photo, full model and serial number, when it appeared, and the result of every published external check
Repair planning
C4 cost planning: The source-listed external check costs €0. A qualified sensor-system diagnosis is generally planned within €140–€320 before any model-specific part is approved.
C4 time plan: 10–20 minutes for the documented C4 external check; allow 30–90 minutes for measured sensor, wiring, and control diagnosis.
Photo of the complete C4 display, Full model and serial number, The exact-model manual for the published external check, No live sensor-circuit test equipment
C4 parts decision: C4 describes heat-exchanger temperature sensor fault; it does not prove the sensor itself has failed. A blocked path, connector, wiring, control input, or the measured condition can produce the same reported area.
What not to do
- Do not bridge, heat, cool, wet, or electrically probe a sensor to clear C4
- Do not replace a sensor until its circuit and the condition it measures have been checked
- Do not run an extra test cycle after the source tells you to stop or arrange service for C4
Preventive maintenance
- 1Follow the exact Daikin maintenance schedule for the air conditioner and keep the model, serial number, and service history available
- 2If C4 begins recurring despite the documented maintenance, stop repeating the same action and request exact-model diagnosis
Frequently asked questions
What exactly does C4 identify?
Daikin identifies it as heat-exchanger temperature sensor fault.
Which action is actually supported for C4?
Do not bridge or electrically probe the sensor circuit; Record the code, switch the air conditioner off, and contact the Daikin service shop; the manual says not to repair, dismantle, reinstall, or modify the unit yourself; Give service the C4 photo, full model and serial number, when it appeared, and the result of every published external check.
Can I run another test after C4?
Not unless the official procedure above explicitly includes it. Complete the safe external actions, then keep the appliance stopped at the service boundary.
Does C4 prove which part failed?
No. It identifies “heat-exchanger temperature sensor fault”; parts are selected only after the exact model and failed function are confirmed.
What information should accompany a service request?
The C4 photo, full model and serial number, the operating stage when it appeared, and the result of each published check.
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