Freezer shows F1 and may not cool properly or may run continuously

Safety first: Disconnect power before accessing internal panels or wiring.

• Locate the freezer thermistor: On most Hitachi upright freezers, the thermistor is clipped to the evaporator cover or wall inside the freezer compartment, often behind a small plastic cover.
• Visual inspection: Check for broken wires, loose connectors, or a thermistor that has come loose from its mounting clip.
• Test the thermistor: Disconnect the thermistor from the harness. Using a multimeter set to resistance (kΩ), measure its value at room temperature (typically 5–20 kΩ depending on model). An infinite or near-zero reading indicates a fault.
• Check harness: Inspect the wiring from the thermistor to the main control PCB for pinched, cut, or corroded wires. Repair or replace as needed.
• Replace thermistor: If readings are out of spec, install a genuine Hitachi freezer thermistor, ensuring it is firmly clipped to the correct location for accurate sensing.
• Control PCB check: If a known-good thermistor still triggers F1, the thermistor input on the main control PCB may be defective and the board should be replaced.