What causes the freezer to defrost by itself?

A freezer may defrost by itself due to a malfunctioning thermostat, which can cause it to overheat. Additionally, a clogged defrost drain or a broken defrost timer can lead to excessive frost buildup, triggering the automatic defrost cycle. External factors, such as frequent door openings or high ambient temperatures, can also contribute to unintended defrosting. Regular maintenance and monitoring can help prevent these issues.