WD Catalog 2018

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Chapter 2 – System Operation
2-8 - -
Heater System Operation
Heater and air conditioner systems both have the same basic function of
moving heat. They take advantage of nature’s laws where heat energy always
moves from a warmer to a cooler area. In a heater system there is no “change of
state” involved in system operation. The system is sealed and operates under
pressure, but the pressure is low when compared to an air conditioner.
A heater system uses the engine coolant to carry excess heat energy to the
cab air. The heart of the system is the water pump. The water pump forces hot
coolant through a hose from the engine block and through the heater core. The
coolant is returned to the engine cooling system either at the suction side of the
water pump or to the radiator.
A control cable, attached to a water valve between the water pump and the
heater inlet, is used to control the flow of coolant to the heater. The heater fan
or blower forces cab air through the heater core where heat energy moves from
the engine coolant to the air in the cab. Figure 2-9 illustrates the main heater
system components. In-cab controls, component housing and air vents are not
shown.
The following heater components are discussed in detail in this section:
1. Heater Core
2. Water Valves
3. Defrosters and Ducts
4. Blowers and Fans
HEATER CORE
FAN CLUTCH
COOLANT LINE
(RETURN)
WATER PUMP
COOLANT LINE
TO HEATER (PRESSURE)
COOLANT (WATER)
VALVE
BLOWER AND
MOTOR
CABLE CONTROL
FROM DASH TO
WATER VALVE
DEFROSTER DUCT
Additional heater controls, ducts, air vents, blend-air doors, temperature regu-
lating devices and auxiliary heaters may be installed as part of a heater
system. These may be air, vacuum, electrical or mechanically operated.
Figure 2-9
This view of a heater system
shows the main components
and how they are connected.