Panasonic CS-RE18NKE Service Manual page 63

15.5.13 H99 (Indoor Freeze Prevention Protection: Cooling or Soft Dry)
Error code will not display (no TIMER LED blinking) but store in EEPROM
Malfunction Decision Conditions
Freeze prevention control takes place (when indoor pipe temperature is lower than 2°C).
Malfunction Caused
Clogged air filter of the indoor unit.
Dust accumulation on the indoor unit heat exchanger.
Air short circuit.
Detection error due to faulty indoor pipe temperature sensor.
Detection error due to faulty indoor unit PCB.
Troubleshooting
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