Evaporator Coil
The indoor coil where refrigerant absorbs heat from your home's air in cooling mode. It sits above the furnace or inside the air handler. A frozen or dirty evaporator coil is one of the most common causes of weak cooling.
The longer answer
The evaporator coil works by allowing refrigerant to evaporate (boil) at low pressure, absorbing heat from the air passing over it. In cooling, warm indoor air crosses the cold coil and sheds heat; in heating mode on a heat pump, the cycle reverses and the indoor coil becomes the condenser, releasing heat indoors.
A dirty coil insulates the refrigerant from the air — reducing heat transfer and raising energy consumption. Annual tune-up cleaning is preventive; a frozen coil (from low airflow, low charge, or a failed defrost) is a shutdown event that needs same-day service, not a wait-and-see.
The Seattle angle
In heating mode on a heat pump, this same coil reverses roles — it's where heat is delivered to your home's air. Keeping it clean matters year-round in Seattle's year-round heat pump duty cycle.
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