Bosch Refrigerator Defrost System Malfunctions
Door left open
If the freezer or refrigerator door was left open for an extended period of time (e.g. more than 4 hours), frost may have accumulated on the food, evaporator coil and around the door opening. The frost should go away after the door is closed and the refrigerator goes through a defrost cycle.
Bosch Refrigerator Defrost Control Board
The defrost control board determines how often to run the defrost cycle. If the board fails, the refrigerator will not go into the defrost cycle. Before replacing the defrost control board, first test the defrost heater and defrost thermostat. If the defrost heater and defrost thermostat are working properly, the defrost control board is likely defective.
Bosch Refrigerator Defrost Timer
The defrost timer turns on the defrost heater several times throughout the day to melt any frost that may have accumulated on the evaporator coils. If the defrost timer is defective, it may not advance into the defrost cycle, or it may not send power to the defrost heater during the defrost cycle. To determine if the defrost timer is defective, slowly advance the dial into the defrost cycle. The compressor should turn off and the heater should turn on. If the timer does not send power to the defrost components or advance out of the defrost cycle within 30 minutes, this indicates that the defrost timer is not advancing. If the defrost timer is not advancing, replace it.
Bosch Refrigerator Door Gasket
A twisted or worn gasket can keep the door from closing properly. Inspect the door gasket for kinks or twists. You can use a hair dryer to try smoothing out the kinks. If the door gasket is damaged it will need to be replaced.
Bosch Refrigerator Defrost Heater Assembly
The defrost heater assembly turns on several times throughout the day to melt away any frost that may have accumulated on the evaporator coils. If the defrost heater assembly is defective, the defrost system will not work, and frost will continue to accumulate on the evaporator coils. To determine if the defrost heater is defective, use a multimeter to test it for continuity. If the defrost heater does not have continuity, replace it.
Bosch Refrigerator Defrost Thermostat
The defrost thermostat monitors the temperature of the evaporator coils. When the coils drop below a set temperature, the thermostat contacts close to allow power to flow to the defrost heater during the defrost cycle. In the defrost cycle, the defrost heater melts away any frost that may have accumulated on the evaporator coils. If the defrost thermostat is defective, the thermostat contacts will not close. As a result, the thermostat won’t provide power to the defrost heater. To determine if the defrost thermostat is defective, use a multimeter to test it for continuity. If the defrost thermostat does not have continuity when it reaches the low temperature of its operating range, replace it.
Bosch Refrigerator Thermistor
A thermistor monitors the temperature of the evaporator coils. If the coils are below a set temperature, the thermistor will alert the defrost control to allow power to flow to the defrost heater during the defrost cycle. In the defrost cycle, the defrost heater melts away any frost that may have accumulated on the evaporator coils. If the thermistor is defective, the defrost control will not be alerted to allow voltage to be sent to the defrost heater.
Bosch Refrigerator Defrost Sensor with Fuse
The defrost sensor monitors the temperature of the evaporator. The defrost sensor has a fuse to back up the sensor in case the sensor fails. If the defrost sensor fails to shut off the defrost heater, the fuse will blow in order to shut off the defrost heater. If the defrost sensor fuse blows, the defrost system will not work, and the refrigerator will not defrost. The defrost sensor fuse is not resettable—if the defrost sensor fuse blows, you must replace the defrost sensor. To determine if the defrost sensor or fuse is defective, use a multimeter to test both the sensor and fuse for continuity. If either the defrost sensor or fuse does not have continuity, replace the defrost sensor.
Bosch Refrigerator Main Control Board
The main control board regulates the power supply to all of the refrigerator components, including the defrost system. If the main control board is defective, it may stop sending voltage to the defrost system. Control boards are frequently misdiagnosed—before replacing the main control, first test all of the defrost system components. If none of the defrost system components are defective, consider replacing the main control board.
Bosch Refrigerator Control Board
The control board regulates the power supply to all of the refrigerator components, including the defrost system. If the main control board is defective, it may stop sending voltage to the defrost system. Control boards are frequently misdiagnosed—before replacing the main control, first test all of the defrost system components. If none of the defrost system components are defective, consider replacing the control board.
Bosch Refrigerator Temperature Sensor
A temperature sensor monitors the temperature of the evaporator coils. If the coils are below a set temperature, the sensor will alert the defrost control to allow power to flow to the defrost heater during the defrost cycle. In the defrost cycle, the defrost heater melts away any frost that may have accumulated on the evaporator coils. If the temperature sensor is defective, the defrost control will not be alerted to allow voltage to be sent to the defrost heater.