Defrost Heater
Function
The defrost heater plays a vital role in automatic defrost refrigerators by melting frost and ice accumulation from the evaporator coils during scheduled defrost cycles. This electrical heating element, typically rated between 200 and 600 watts depending on refrigerator size, is strategically positioned near or within the evaporator coil assembly to provide targeted heat application. The heater activates when the defrost timer or control board initiates a defrost cycle, temporarily raising the temperature around the evaporator coils above freezing to melt accumulated frost.
Most defrost heaters consist of a resistive heating element enclosed in a protective metal sheath or glass tube to prevent moisture damage and ensure safe operation in the humid freezer environment. The heating element may be configured as a straight rod, coiled element, or shaped specifically to match the evaporator coil configuration for optimal heat distribution. Some advanced systems use multiple heaters or variable-output heaters that can adjust heat intensity based on frost accumulation levels.
The defrost heater operates in coordination with other defrost system components, including the defrost timer, defrost termination switch, and drain heater. During a typical defrost cycle, the heater activates for a predetermined time or until the defrost termination switch senses that all frost has melted. The melted water drains through a defrost drain system where it may be further heated by a drain heater before flowing to an evaporation pan beneath the refrigerator.
Symptoms of a Broken Defrost Heater
A failed defrost heater creates distinctive symptoms primarily related to frost and ice accumulation. The most obvious sign is excessive frost buildup on the evaporator coils, which appears as a thick layer of white ice covering the coil fins and blocking airflow. This condition gradually worsens over time as each defrost cycle fails to remove accumulated frost, eventually leading to a solid block of ice encasing the entire evaporator assembly.
As frost accumulation increases, you’ll notice reduced cooling efficiency throughout the refrigerator. The unit may run continuously as it struggles to maintain proper temperatures, and fresh food compartments may not stay adequately cold. Freezer temperatures may actually rise because ice-blocked evaporator coils cannot effectively transfer heat from the freezer air.
Other symptoms include water accumulation in the freezer compartment, particularly around the bottom or on shelves, as frost melts during periods when the freezer door remains open for extended times. You may also notice unusual noises from the evaporator fan motor as it struggles to move air through ice-blocked coils. In severe cases, the refrigerator may stop cooling entirely as complete ice blockage prevents any air circulation through the evaporator.
Repair Solutions
Diagnosing a defrost heater requires accessing the evaporator compartment, which typically involves removing panels inside the freezer section. Before beginning any work, unplug the refrigerator and remove all food items from the freezer. Locate the evaporator coils and heater assembly, noting the extent of frost accumulation and the heater’s physical condition.
Visual inspection often reveals obvious defrost heater problems such as cracked glass tubes, broken heating elements, or damaged electrical connections. Look for signs of arcing, burning, or corrosion around the heater terminals. If the heater appears physically intact, electrical testing is necessary to confirm proper operation.
Test the defrost heater using a multimeter set to resistance mode. Disconnect the heater’s electrical connections and measure resistance across the heating element terminals. A functional heater should show continuity with resistance typically ranging from 15 to 50 ohms depending on wattage rating. No continuity indicates a broken heating element, while very low resistance might suggest a short circuit condition.
If the heater tests faulty, replacement is the only repair option since heating elements cannot be repaired. Before installing a new heater, completely defrost the evaporator area using a hair dryer or by leaving the refrigerator unplugged with doors open until all ice melts. This process may take several hours but is essential for proper heater installation and system operation.
Install the replacement heater in the exact same position and orientation as the original, ensuring proper clearance from evaporator coils and adequate support to prevent vibration damage. Reconnect electrical connections securely, making sure terminals are clean and tight. After installation, manually initiate a defrost cycle to verify proper heater operation, then monitor the refrigerator through several automatic defrost cycles to ensure the heating system maintains frost-free evaporator coils.