Why Does Frost Build Up in Direct Cool Refrigerators?

Frost build up is a common issue in direct cool refrigerators, also known as "frost-free refrigerators." In these units, the evaporator coils are directly exposed on the exterior of the fridge. As the evaporator absorbs heat from inside the fridge, moisture from the air condenses and freezes on the evaporator coils, leading to frost accumulation.

To reduce frost build up, some direct cool refrigerators now feature an automatic defrost module. This helps balance the internal and external air pressure when the door is opened, reducing the influx of humid air from outside. However, some frost will inevitably form as a result of the direct cool system.

Why Don't Forced Air Refrigerators Frost Over?

In forced air or "frost-free" refrigerators, the cooling system relies on fans circulating air rather than exposed evaporator coils. The evaporator and condenser coils are contained within the insulated body of the fridge.

The fan motor is mounted near the evaporator coils in the freezer compartment. When the compressor runs, the fan also switches on to force convection currents and distribute the cold air throughout the fridge and freezer cavities. This leads to uniform cooling and temperature distribution.

Frost does form on the evaporator coils but is not visible to the user. Most forced air fridges use an automatic defrost mechanism to periodically melt away accumulated frost. The fridge pauses cooling, activates heating elements near the coils, and the melted frost drains away or evaporates. This auto-defrost cycle happens automatically without any user intervention.

So while forced air fridges are termed "frost-free," frost does build up internally on coils. The user simply doesn't see it due to the contained cooling system design.

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