What Is an Evaporator Coil?

The evaporator coil sits inside the refrigerator or freezer compartment, usually hidden behind a rear panel. Cold liquid refrigerant expands and evaporates inside it, absorbing heat from the air a fan circulates past it — that's the actual cooling step in the cycle.

A light layer of frost is normal; a solid block of ice covering the coil is not. Heavy icing usually points to a failed defrost cycle, a blocked drain, or a door seal letting in warm, humid air. Once the coil ices over completely, airflow stops and the whole unit stops cooling evenly, even though the compressor is still running.

Frequently Asked Questions

Is a little frost on the evaporator coil normal?

Yes — a light, even frost is part of normal operation. What's not normal is a thick, solid layer of ice covering the coil, which blocks airflow and usually points to a failed defrost cycle, a blocked drain, or a door seal letting in warm, humid air.

Why is only part of my evaporator coil frosting over?

Frost on only a section of the coil, rather than evenly across it, can be a sign of a sealed-system problem such as a refrigerant leak, but other causes exist, which is why a diagnostic confirms it before anything is replaced.