F4
Carrier Split AC
Severity: ModerateWhat Does This Error Mean?
F4 on a Carrier AC means the outdoor coil (condenser pipe) temperature thermistor has a fault. This sensor monitors the outdoor heat exchanger temperature to protect the compressor and regulate the refrigerant cycle. A failed or disconnected thermistor triggers F4 and the compressor stops.
Affected Models
- Carrier Ester Plus
- Carrier Superia Plus
- Carrier Durafresh Neo
- Carrier Inverter Split AC (all models)
- Carrier Ductable AC (inverter series)
Common Causes
- Outdoor coil thermistor failed — resistance reading outside the normal operating range
- Thermistor clip detached from the outdoor condenser coil pipe
- Thermistor wiring broken or corroded from weather exposure
- Connector at the outdoor PCB loose or moisture-damaged
- Outdoor PCB fault causing incorrect thermistor reading
How to Fix It
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Power off the AC at the remote and circuit breaker. Wait 5 minutes and restart.
If F4 clears and the AC runs normally, monitor for recurrence. A persistent F4 confirms the thermistor has failed.
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Ensure the outdoor unit has full clearance on all sides.
An obstructed outdoor unit overheats the condenser coil, pushing the thermistor reading toward the fault threshold — especially if the sensor is already slightly degraded.
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Call Carrier service (1800-103-9999) if F4 persists.
Mention that the error is F4 when booking — this helps the technician bring the correct sensor for your model.
When to Call a Professional
F4 requires a Carrier authorised technician. Do not open the outdoor unit — high-voltage capacitors are present. Carrier India customer care: 1800-103-9999.
Frequently Asked Questions
How much does Carrier F4 repair cost in India?
An outdoor coil thermistor typically costs Rs 300–700. With the Carrier service visit charge and labour, total repair is usually Rs 1,200–2,500. Under warranty, parts and labour are covered at no charge.