WD Catalog 2018

869 / 1003

5-7 - -
Heater Controls
HEATER CORE
FAN CLUTCH
COOLANT
LINE RETURN
(LOW PRESSURE)
WATER PUMP
COOLANT LINE
TO HEATER (PRESSURE)
COOLANT (WATER)
VALVE
BLOWER AND
MOTOR
CABLE TO
WATER VALVE
DEFROSTER DUCT
HOT TEMPERATURE
CAB AIR DIRECTION
COOL
DEF
FAN
OFF
CABLE TO
DUCT DOOR
(HEAT/DEFROST)
CIRCUIT TO BLOWER
HEATER SYSTEM CONTROL PANEL
SLIDE CONTROL
LEVERS
A water valve is the primary control for a basic heater system. When the
valve is open, hot engine coolant flows through the heater core and back to
the engine. The driver can adjust the control to modulate coolant flow
through the heater core.
In some heater system designs, temperature control is achieved by
allowing part of the air moving through the heater duct system to bypass
the heater core. The amount of bypass air is controlled by a door. This
design is commonly called a blend air system. A water valve is sometimes
included in the design and directly linked to the door control.
Another cable operates a door inside the duct system and directs air
flow through defroster ducts to the windshield. The knob controlling the
blower motor switch may be set to one or more speed positions, or off. This
switch controls the air velocity (CFM) through the duct system and heater
core.
Note: Air pressure, electric actuators or vacuum may be
used in place of cable controls. The air pressure or
vacuum do not automatically adjust system function.
Manual controls, air switches or other automatic elec-
trical controls regulate vacuum and control air pres-
sure to adjust system function.
Figure 5-5
Typical heater system con-
trols and locations are
shown and described in this
drawing.