F4
Panasonic Split AC
Severity: ModerateWhat Does This Error Mean?
F4 on a Panasonic AC means the outdoor pipe temperature thermistor has a fault. This sensor monitors the temperature of the outdoor heat exchanger pipe during operation to protect the compressor and regulate refrigerant flow. A failed or disconnected thermistor triggers F4 and the system stops.
Affected Models
- Panasonic Inverter Split AC (all capacities)
- Panasonic CS-SU series
- Panasonic CS-YU series
- Panasonic CS-XU series
- Panasonic NanoeX series
Common Causes
- Outdoor pipe thermistor failed — resistance outside specification
- Thermistor clip dislodged from the outdoor heat exchanger pipe
- Thermistor wiring corroded or broken from UV or moisture exposure
- Connector at the outdoor PCB loose or moisture-damaged
- Outdoor PCB fault misreading the pipe sensor signal
How to Fix It
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Power off at the remote and circuit breaker. Wait 5 minutes and restart.
If F4 clears after a reset and does not return, it was a transient error. If F4 returns within a few minutes, the thermistor has genuinely failed.
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Check the outdoor unit has full ventilation clearance on all sides.
Ensure at least 30 cm clearance. An obstructed outdoor unit overheats the heat exchanger and can push a marginal thermistor into fault range.
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Note when F4 appears — immediately on startup or after the system runs for a while.
Immediate F4 = broken wire or disconnected connector. F4 after running = thermistor drifts out of range as the outdoor unit heats up.
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Call Panasonic service (1800-103-1333) if F4 persists.
The outdoor pipe thermistor is typically a low-cost repair — the main expense is the service visit fee.
When to Call a Professional
F4 requires a Panasonic authorised technician — do not open the outdoor unit. Panasonic India: 1800-103-1333. The technician will test the outdoor pipe thermistor resistance using the service manual specification chart.
Frequently Asked Questions
What is the difference between Panasonic F3 and F4?
Both are outdoor unit thermistor faults, but they monitor different locations. F3 is typically the outdoor heat exchanger (coil) thermistor — it clips to the coil fin area. F4 is the outdoor pipe thermistor — it monitors a specific pipe (discharge or liquid line) on the outdoor unit. A technician with the Panasonic service manual will confirm which sensor applies to your specific model.