WD Catalog 2018

4-15

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Evaporator Coil

Evaporator Coil

Evaporator coils come in various shapes and sizes. Most are of fin and tube

construction. The fins and tubing are designed to transfer heat from the cab air

to the cool refrigerant vapor as it moves through the evaporator tubing. The

fins are colder than the cab air, so moisture in the air blown across the coil

condenses on the fins. The moisture forms into droplets and drains to the

bottom of the evaporator housing and out of the cab through a drain tube. Dust

or other airborne particles may also be trapped in the condensed moisture

droplets. In this way the AC system dehumidifies, filters and cools the air in the

cab.

Refrigerant enters the evaporator coil, expands rapidly and changes state

(drops in temperature and pressure). The refrigerant absorbs heat energy from

the air in the cab and moves through the tubing to exit the evaporator coil. A

variety of expansion valve or other refrigerant flow regulating devices (de-

scribed earlier) are used in an AC system design, at the inlet to and/or the

outlet from the evaporator coil. Each is designed to control the flow of refriger-

ant to provide maximum heat transfer in the evaporator. The drawing, Figure

4-12, is a cutaway view of a typical evaporator coil.

EVAPORATOR

EXPANSION VALVE

COLD LOW PRESSURE GAS

THERMOSTAT

METERED REFRIGERANT

CAB AIR

FLOW

Air Conditioner Blower/Fan and Motor Assembly

In HVAC system designs, a blower assembly is positioned to move air through

the evaporator coil and heater core. For efficient air movement, the air must be

confined within a housing. The blower assembly used in a system may be

located for functional or space considerations. Some pull air and others push

air through evaporator and/or heater fins.

Fans are used to move air through the fins of the condenser. In underhood

applications the engine cooling fan is used. Roof or remote mounted condensers

have separate fan/motor assemblies.

Figure 4-12

The evaporator coil illus-

trated is mounted inside an

enclosure (not shown) de-

signed for efficient air flow

between the fins of the

evaporator.