Display shows E4 and the defrost cycle does not operate correctly (excessive ice or no defrost).

Warning: Defrost circuits involve mains voltage. If you are not comfortable working with electrical components, contact a qualified technician.

• Unplug the cooler: Always remove power before testing continuity or accessing the evaporator area.
• Access evaporator and defrost components: Remove the interior rear panel to expose the evaporator coil, defrost heater (often an aluminum or glass-encased element), and defrost sensor.
• Inspect for damage: Look for burnt spots on the heater, broken wires, or a sensor that has come loose from the coil.
• Test heater continuity: Disconnect heater leads and measure resistance with a multimeter. A typical heater will show finite resistance (e.g., 50–300 Ω). An open circuit means the heater is failed.
• Test defrost sensor: Measure resistance of the defrost sensor (often the same as the evaporator NTC or a separate sensor). Compare to spec; replace if open/shorted.
• Check wiring to PCB: Inspect the harness from heater and sensor back to the main control PCB for burns, loose connectors, or corrosion.
• Replace faulty parts: Install a new Blastcool defrost heater or Blastcool defrost/evaporator sensor as required. Ensure all connections are tight and insulated.
• Reassemble and test: Refit panels, restore power, and allow the unit to run through at least one defrost cycle. Monitor for normal frost and drainage.

If E4 persists with good heater and sensor, the defrost relay or control logic on the main PCB may be defective and should be replaced by a professional.