The most common symptom of defrost problem in your refrigerator is a complete and uniformly frosted evaporator coil. Frost may also be seen on the panel covering the evaporator or cooling coil. During the refrigeration cycle of a refrigerator, moisture in the air freezes and sticks to the evaporator coils as frost The refrigerator has to go through a defrost cycle to melt this ice that continues to build up on the evaporator coils from the moisture in the air. If the refrigerator has a defrost problem the frost collected on the coils will not melt. Sometimes frost builds up to the point that it blocks airflow and the refrigerator stops cooling completely.
Refrigerator defrost problem is difficult to fix and most of the time require a refrigerator repair expert to identify the root of the problem.
Reasons behind refrigerator defrost problem
Faulty defrost timer
In any frost free refrigerator there is a defrost system which controls the cooling and defrost cycle. The components of the defrost system are: a defrost timer and a defrost heater. A defrost timer switches the refrigerator between the cooling and defrost mode. If it goes bad and stops at cooling mode, it causes excessive frost to build up on the evaporator coils which reduces the air flow. Or when it stops at the defrost mode it melts all the frost and does not go back to the cooling cycle. A broken defrost times prevents the refrigerator from cooling efficiently.
Defective defrost heater
A defrost heater melts the frost developed over the evaporator coil. But if it goes bad frost does not melt and excessive frost accumulates on coils reducing the cool air flow inside the refrigerator.
So when either of the 2 components i.e. defrost timer or defrost heater go faulty, the fridge does not understand when to cool and when to defrost.
If the refrigerator does not defrost, the defrost thermostat might be defective. In a defrost system, the defrost heater turns on several times in a day to melt away the frost developed on the evaporator coil. This defrost heater is connected to a defrost thermostat. The defrost thermostat senses the temperature of cooling coils. When the cooling coils become cold enough, thermostat sends signal to defrost heater to turn on. If the thermostat is defective it may not be able to sense the temperature of coils and then won’t turn on the defrost heater. If the defrost heater doesn’t turn on, the refrigerator will never start the defrost cycle and will eventually stop cooling.
The above are some common reasons behind refrigerator not defrosting problem but there can be other reasons as well.