Less common but still possible. A sudden power loss, CMOS battery failure, or a malicious BIOS update can corrupt storage configuration settings. The BIOS might:

The motherboard of your air conditioner processes all data. If the PCB is damaged due to a power surge, moisture, or a bug shorting it out, it may misinterpret signals from the sensors, resulting in an E79 code.

The fuser is either not heating when it should, or the sensor is reporting a value outside the expected range (e.g., below 0°C or above 300°C instantly).