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In a self-defrosting freezer, poor cooling often results from a heavy frost build-up on the evaporator coils. You can't see these coils without removing a panel inside your freezer. But if you see any frost or ice build-up on the inside walls, ceiling, or floor of your freezer, it's a sure sign of frost build-up. And that's a sign of a problem with the self-defrosting system.
Freezers should self-defrost three to four times in 24 hours. But if a component in the self-defrosting system fails, the freezer continues to try to cool, instead. Eventually, so much frost builds up on the evaporator coils that the circulating fan can't draw air over the coils. There's still some cooling because the coils are frozen. But with no air flow over the coils, the cooling is quite limited and the freezer isn't as cold as it needs to be.
An easy (though often inconvenient) test of whether the problem is with the self-defrosting system is to remove all of the perishable food from the freezer, turn the thermostat to Off, and leave the door open for 24 to 48 hours. (Keep several towels handy in case the melting frost and ice overflows the drip pan). This "manually" defrosts the freezer. When the frost and ice build-up has completely melted away, turn the thermostat back to a normal setting. If the freezer then cools properly, it indicates a problem with one of these components in the self-defrosting system:
- The defrost timer. To test this, manually advance to the defrost cycle. The unit should advance itself out of the defrost cycle in about 45 minutes.
- The defrost thermostat (or bi-metal switch). This thermostat allows current to pass through it at temperatures of 20 to 30 degrees Fahrenheit and prevents current from passing through it at 40 to 60 degrees (depending on its design). This is difficult to test, though, because it takes a prolonged, very-cold temperature to turn it on.
- The defrost heater. You can test this for continuity using an electrical meter.
