Evaporator Coils

Evaporator coils … 101

An evaporator coil is the part of an air handler or furnace or heat pump system that becomes cold when the unit operates in cooling or becomes warm for a heatpump in winter. Evaporator coils are mounted inside air handlers or on top of furnaces and are connected to the duct system.  Air is conditioned as it flows past the evaporator coil and then distributed by the duct system.Evaporator coils must be sized properly or “matched” with the outside condenser, indoor blower and duct system.Refrigerant is metered as it enters the evaporator coil by use of a thermal expansion valve, electronic expansion valve or piston type metering device.  The metering device causes a restriction in the refrigerant cycle producing a change in the refrigerant’s pressure and temperature inside the evaporator coil. The refrigerant pulls heat from the metal that makes up the evaporator coil in cooling and the metal evaporator coil in turn pulls heat from the air flowing thru the small fins that make up the coil.

If the evaporator coil becomes dirt or clogged, the dirt act as insulation, preventing heat transfer and as an obstruction, slowing or prevent proper air flow.

As warm air passes over the cold evaporator coil in cooling, the moisture in the air condenses into water and runs off the evaporator coil.  The water is collected in a condensate drain pan and drained away. It is this psychrometric process allows properly sized, maintained and operated cooling systems to control the indoor humidity and comfort levels inside your home.

Using our Total Performance Diagnostic program, AirOne is able to quickly evaluate the condition and properties of the evaporator coil, the air flow conditions and heat transfer properties to verify proper system operation.