Chevrolet Light Duty Truck 1973 Service Manual page 29

BLOWER AND AIR INLET ASSEMBLY
The blower and air inlet assembly draws outside air
through the outside air inlet grille located forward of the
windshield reveal molding and channels the air into the
heater distributor assembly. The operation of the blower
motor is controlled by the FAN switch on the heater
control. The motor is connected in series with the FAN
switch and also the blower resistor assembly. Located in
the fuse block, in series between the blower motor and
the battery, is a 25 amp. fuse C-K models - a 20 amp
fuse on G models.
HEATER DISTRIBUTOR ASSEMBLY
The heater distributor assembly houses the heater core
and the doors necessary to control mixing and
channeling of the air. Since the unit has no water valve,
water circulation keeps the core hot at all times. That
portion of the air passing through the core receives
maximum heat from the core. Air entering the
distributor assembly is channeled as follows:
C-K Models
Air entering the distributor can be directed out the purge
door opening, on the right end of the distributor
assembly, by the purge door. If the purge door is closed,
then air is directed through and/or around the heater
core by the temperature door. Air is then directed into
the passenger compartment through the heater (floor)
outlets and/or the defroster (dash) outlets by the
defroster door. The temperature of the outlet air is
dependent on the ratio of heated to unheated air
(controlled by the temperature door).
G Models
Airflow is controlled by three doors in the distributor
assembly. The air door can be adjusted to vary airflow. If
air is allowed to enter the distributor assembly, it is then
directed through and/or around the heater core by the
temperature door. Air is directed into the passenger
compartment through the heater (floor) and/or defroster
(dash) outlets by the defroster door. The temperature of
the outlet air is dependent on the ratio of heated to
unheated air (controlled by the temperature door).
CONTROLS
C-K Models (Fig. 2)
These controls are mounted in the center of the dash,
above the radio assembly. The control incorporates two
levers which make use of bowden cables to control
positioning of the purge, temperature and defroster
doors.
Temperature Lever
This lever controls the positioning of the TEMPERA-
THEORY OF OPERATION
TURE door in the heater distributor assembly. All
incoming "outside" air is directed around the heater core
in the COLD position or through the core in the HOT
position. The desired outlet temperature is obtained by
blending the heated and unheated air according to the
setting of the temperature lever.
Heater-Def Lever
The HEATER-DEF lever controls the position of the
DEFROSTER door and the PURGE door. In the OFF
position, the blower is "on" and incoming air is directed
up under the dash through the purge door opening. As
the lever is moved to the right of the OFF position, the
door closes, directing airflow on into the distributor
assembly. With the lever at HEATER, the DEFROSTER
door directs almost all airflow to the heater (floor) outlets
- a small amount of air is directed to the defroster (dash)
outlets. In the DEF position, most airflow is diverted to
the defroster outlets. Moving the lever part way, as
desired, will split airflow between the floor and defroster
outlets.
Fan Control
The blower fan lever is located at the left hand side of
the control assembly. The blower motor will operate as
soon as the ignition switch is turned to the RUN
position. The control has three positions only; LO, MED,
HI. There is no OFF position.
G Models (Fig. 3)
The controls are located in the instrument panel, just to
the right of the instrument cluster. In operation, two
levers control all heating operations.
HEATER A N D AIR C O N D IT IO N IN G
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OFF
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FAN
Fig. 2-Heater Control--C-K Models
Fig. 3-Heater Control-G Models
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HEATER
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LIGHT DUTY TRUCK SERVICE MANUAL