Freezer displays E4 and may stop defrosting properly, leading to ice buildup on the evaporator.

Safety first: Unplug the freezer. The defrost heater operates at mains voltage; do not test live unless you are qualified.

• Access evaporator and heater: Remove baskets and inner rear panel to expose the evaporator coil. The defrost heater is usually a metal or glass-encased element at the bottom or woven through the coil.
• Visual inspection: Look for burnt spots, broken heater tubes, or melted connectors. Check the defrost thermostat/thermal fuse clipped to the evaporator tubing.
• Test heater continuity: Disconnect heater leads and measure resistance with a multimeter. A typical heater will show finite resistance (e.g., 50–300 Ω). If open (OL), replace the heater.
• Test defrost thermostat/fuse: At freezer temperature, the defrost thermostat should be closed (low resistance). If it is open when cold, it is faulty. Thermal fuses should always show continuity; if open, replace.
• Inspect wiring and connectors: Repair any burnt or loose connectors with proper high-temperature-rated terminals.
• Reassemble and test: Replace faulty components with Hisense-compatible parts, reassemble the rear panel, restore power, and monitor for normal defrost operation and clearing of E4.

If all defrost components test good, the main control board defrost relay or logic may be defective and should be checked by a technician.