Freezer displays F4, may not defrost, heavy ice buildup on evaporator and poor cooling.

Safety: Disconnect mains power before testing heater circuits. The defrost heater operates at full line voltage.

Procedure:

• Access evaporator: Remove food, baskets, and the rear interior panel to expose the evaporator and defrost components.
• Inspect for ice: If the evaporator is encased in solid ice, the defrost system is likely not operating.
• Test defrost heater: Disconnect the heater leads and measure resistance with a multimeter. Typical values are 20–150 Ω depending on design. An open circuit (OL) indicates a failed heater.
• Check defrost thermostat / thermal fuse: Many Fisher & Paykel freezers use a defrost thermostat or thermal fuse in series with the heater. Test for continuity at freezing temperatures; an open device will prevent heater operation.
• Wiring and connectors: Inspect the harness from heater/thermostat to the main control board for burns, loose connectors, or broken wires. Repair as needed.
• Control board: If heater and safety devices test good, the main control board defrost relay or triac may be faulty. Replace the main control board if no power is supplied to the heater during a forced defrost (technician function).
• Defrost manually: After repair, fully defrost the evaporator with the unit unplugged and towels in place to catch water.