- HVAC
- Air conditioner
C4
Daikin room AC C4: heat-exchanger temperature-sensor problem
Evidence linked to this decision
View source: Daikin FTXJ-A installer reference guide — EnglishRisk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
C4 means heat-exchanger temperature-sensor problem in the cited model family. Do not buy a part from the display. First record whether the code appears immediately at room temperature or only after the coil changes temperature. Immediate recurrence supports an open/short input; later drift can be poor contact or a real thermal condition.
Safety first
Stop and check this first
- Burning smell, smoke, sparking, water near electricity, severe icing or repeated breaker trips means leave the system off. Never open electrical panels or loosen refrigerant pipework.
Safe checks you can perform
- Capture the failure pattern before clearing it
- Run the safe discriminating check
- Use recurrence as the decision point
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measured service test for C4
What a technician must be able to justify
A technician is coming
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Measured service test for C4
What they doCompare thermistor resistance and measured temperature through the service table, including connector and seating.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Capture the failure pattern before clearing it
Photograph C4, both exact model identifiers and the operating state. Record whether the code appears immediately at room temperature or only after the coil changes temperature.
Burning smell, smoke, sparking, water near electricity, severe icing or repeated breaker trips means leave the system off. Never open electrical panels or loosen refrigerant pipework.
Evidence: Daikin FTXJ-A installer reference guide — English
Run the safe discriminating check
Stay outside sealed or powered compartments. Immediate recurrence supports an open/short input; later drift can be poor contact or a real thermal condition. If the observation is unclear, stop and treat the internal branch as unresolved.
Burning smell, smoke, sparking, water near electricity, severe icing or repeated breaker trips means leave the system off. Never open electrical panels or loosen refrigerant pipework.
Evidence: Daikin FTXJ-A installer reference guide — English
Use recurrence as the decision point
Only if the exact user manual permits it and no stop condition exists, make one controlled attempt. If C4 returns, stop; repeated resets destroy evidence and can worsen the fault.
Burning smell, smoke, sparking, water near electricity, severe icing or repeated breaker trips means leave the system off. Never open electrical panels or loosen refrigerant pipework.
Evidence: Daikin FTXJ-A installer reference guide — English
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Virtual technician
Does C4 still appear after these checks?
This guided flow uses the exact code and your answers to choose a test, an expected result and the next branch.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- HVAC
- Brand
- Daikin
- Product type
- Air conditioner
Known code variants
- aire acondicionado Daikin C4
- climatisation Daikin C4
- climatizzatore Daikin C4
- code erreur C4 Daikin
- codice C4 Daikin
- código C4 Daikin
- Daikin AC C4
- Daikin C4
- Daikin error C4
- Daikin Fehler C4
- Daikin Fehlercode C4
- error C4 Daikin
- errore C4 Daikin
- Klimaanlage Daikin C4
- panne C4 Daikin
What it means
Daikin's official regional documentation associates C4 with heat-exchanger temperature-sensor problem. That is the controller's observed condition, not a universal failed component. Confirm the exact model before using this decision path; the same code can mean something else on another product family.
Warnings and stop conditions
- Highsource verified
Burning smell, smoke, sparking, water near electricity, severe icing or repeated breaker trips means leave the system off. Never open electrical panels or loosen refrigerant pipework.
Evidence: Daikin FTXJ-A installer reference guide — English
Symptoms and causes
Probable causes · in order
- First branch to separate: temperature feedback implausible for the operating statePossible
The documented condition is heat-exchanger temperature-sensor problem. Discriminating observation: Record whether the code appears immediately at room temperature or only after the coil changes temperature. Expected reading and decision: Immediate recurrence supports an open/short input; later drift can be poor contact or a real thermal condition.
Evidence: Daikin FTXJ-A installer reference guide — English
- If that branch is ruled out: thermistor seating, harness or control-input faultPossible
thermistor seating, harness or control-input fault remains possible only after the safe observation is recorded. The next evidence is measured, not another reset: Compare thermistor resistance and measured temperature through the service table, including connector and seating.
Evidence: Daikin FTXJ-A installer reference guide — English
Sources and technical references
- 1
Daikin FTXJ-A installer reference guide — English
Daikin Europe N.V. · 2022 · official_doc
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