Proline freezer shows E4 and may not defrost properly, leading to ice buildup on the evaporator.

Safety first: Disconnect power before accessing the evaporator or defrost components. Beware of sharp metal edges.

Steps to address E4:

• 1. Access evaporator area: Remove baskets and the inner rear panel to expose the evaporator coil and defrost components.
• 2. Locate defrost sensor/thermostat: This may be a clip-on thermostat (round metal disc) or an NTC sensor attached to the evaporator tubing.
• 3. Inspect for ice and displacement: Check if the sensor is buried in ice or has come loose from the coil. If loose, reattach firmly. If heavily iced, fully defrost the unit (doors open, towels down) before testing.
• 4. Test the defrost thermostat (if fitted): At freezing temperatures, it should show continuity (low resistance). Warm it gently with your hand or a hairdryer (on low, at a distance) and confirm it opens (no continuity). Replace if it remains open or closed in all conditions.
• 5. Test NTC-type defrost sensor: Disconnect and measure resistance; compare to expected NTC values. Replace if open, shorted, or out of range.
• 6. Check wiring: Inspect the harness from the sensor/thermostat to the control PCB for damage or loose connectors.
• 7. Replace faulty parts: Install a compatible Proline defrost thermostat or defrost NTC sensor, clip it securely to the evaporator, and route wiring correctly.

When to call a technician: If the sensor and wiring are good but E4 persists, the main control PCB may not be driving the defrost cycle correctly and should be professionally evaluated.