WD Catalog 2018

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Chapter 3 - Heater Components and Controls
3-4 - -
A large capacity heater core has more tubes and more fin area so that
more coolant can circulate through the tubes and more air moves through
the fins. The result is more heat energy transfer to the air in the cab.
2. Heater System Ducts
Ducts direct and control air as it circulates through the heating system.
The heater core housing is usually part of the duct system as is the blower
or fan assembly. Air outlet duct openings are usually located close to the
floor. The outlets are positioned to direct warm air to the feet and body of
the occupants.
All heater/defroster systems pick up some outside air and mix it with
cab air. They often have doors inside the duct system to regulate, mix or
restrict air flow as part of the heater control system. Many heater systems
use 100% outside air. Only auxiliary heaters use 100% cab air. Figure 3-5
illustrates typical heater system ducts with heater components. The
arrows indicate the air flow pattern through the duct system. This view of
a typical heater system does not include heater hoses, clamps, a water
valve or controls.
TO DEFROSTER
VENTS
MOTOR & BLOWER ASSEMBLY
OUTSIDE AIR
CAB AIR
HEATER CORE
TO FLOOR
VENTS
HEAT–DEFROST
DOOR IN
DEFROST
(CABLE
CONTROLLED) TEMPERATURE BLEND
AIR DOOR
(CABLE CONTROLLED)
3. Blower or Fan and Motor Assembly
Air movement in a heater system depends on the blower or fan. The
operator selects the motor speed to control the amount of air circulated
through the system. Motors have one to four speeds, depending on heater
design. Both single and double entry blower wheels are used. Figure 3-6
shows and describes typical motors, blower wheels, and a fan.
Figure 3-5
The drawing illustrates the
relative position of the
heater core, a (pull through)
motor and blower assembly,
and two doors inside the
duct system. These doors
control air mixing at the
inlet side of the system and
direct the air to the cab and
defroster vents.