There are a few potential reasons why an automatic defrost fridge/freezer may stop defrosting and start freezing again after working fine for years, even without any changes to its environment. Some possibilities include:
Malfunctioning Defrost Timer: Automatic defrost fridges/freezers typically have a defrost timer that controls the defrosting cycle. If the defrost timer becomes faulty or stops working altogether, it can disrupt the defrosting process. This can lead to excessive ice buildup in the freezer compartment and cause the unit to freeze instead of defrosting as intended.
Defective Defrost Heater or Thermostat: The defrost heater or defrost thermostat within the appliance may fail over time. The defrost heater is responsible for melting the ice buildup during the defrost cycle, while the defrost thermostat monitors the temperature to ensure proper operation. If either of these components becomes defective, the unit may not defrost correctly, resulting in freezing instead of proper defrosting.
Blocked or Faulty Defrost Drain: A clogged or faulty defrost drain can prevent melted ice from properly draining out of the appliance during the defrost cycle. This can lead to water accumulation and subsequent freezing within the unit.
Insufficient Air Circulation: If there is a problem with the fan or the vents that circulate air within the appliance, it can affect the distribution of cold air and cause uneven cooling. This can lead to freezing in some areas while others remain at the desired temperature.
In such cases, it is advisable to contact a professional appliance technician who can diagnose the specific issue and provide the necessary repairs or replacements. They can inspect the defrost timer, defrost heater, defrost thermostat, and other relevant components to identify the root cause of the problem and restore the proper functioning of the appliance.