Display shows E4 and the refrigerator may not defrost, leading to frost buildup on the evaporator and poor cooling.

Safety: Unplug the refrigerator before working in the freezer compartment. Water from defrosting can create slip hazards—use towels and a tray.

Steps:

• 1. Confirm symptoms: Check for heavy frost on the evaporator cover or back wall of the freezer. If present, a defrost issue is likely.
• 2. Access defrost sensor: Remove freezer drawers and the rear panel to expose the evaporator. The defrost sensor is typically clipped to the evaporator tubing near the top or middle.
• 3. Inspect sensor and clip: Ensure the sensor is tightly clipped to the tubing and not hanging loose. Look for cracked insulation or broken wires.
• 4. Test sensor: With power disconnected, unplug the sensor and measure resistance. Compare to the NTC chart at the current coil temperature. If the sensor reads open, shorted, or far out of range, replace it.
• 5. Check wiring: Inspect the harness from the sensor to the main PCB for damage or corrosion. Repair any bad connections.
• 6. Replace sensor if needed: Install a new Haier defrost sensor/thermistor, clip it firmly to the evaporator tube, and route wires away from the heater and fan.
• 7. Verify defrost operation: After reassembly and restoring power, force a defrost cycle if your model allows (consult service manual) or monitor over 24–48 hours to ensure frost does not reaccumulate.

Warning: Do not bypass or short the defrost sensor; this can overheat the evaporator and create a fire risk.