Chevrolet 1977 light duty truck, Service Manual

Page: 31 / 861

BLOW ER A N D AIR IN LET ASSEMBLY
T h e blower and air inlet assembly draws outside air
thro u g h the outside air inlet grille located forw ard o f the
w indshield reveal m olding and channels the air into the
h e a te r distributor assembly. The operatio n of the blower
m otor is controlled by the F A N switch on the heater
control. The m otor is connected in series with the F A N
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 am p
fuse on G models.
H E A TE R D IS T R IB U T O R ASSEM BLY
T h e heater distributor assembly houses the heater
core an d the doors necessary to control mixing and
c h a n n e lin g o f the air. Since the unit has no w ater valve,
w ater circulation keeps the core hot at all times. T hat
portio n o f the air passing through the core receives
m a x im u m heat from the core. Air entering the
d istrib u to r assembly is channeled as follows:
C-K M odels
A ir entering the distributor can be directed out the
purge door opening, on the right end o f the distributor
assembly, by the purge door. If the purge door is closed,
then air is directed through a n d / o r a ro u n d the heater
core by the tem p eratu re door. A ir is then directed into
the passenger co m p a rtm e n t through the heater (floor)
outlets a n d / o r the defroster (dash) outlets by the
defro ster door. The tem perature o f the outlet air is
d e p e n d e n t on the ratio o f h eated to unheated air
(controlled by the tem p eratu re door).
G M odels
A ir flow is controlled by three doors in the
distrib u to r assembly. The air d oor can be adjusted to
vary airflow. If air is allowed to enter the distributor
assembly, it is then directed through a n d / o r a round the
h e a te r core by the tem p eratu re door. A ir is directed into
the passenger co m p a rtm e n t through the heater (floor)
a n d / o r defroster (dash) outlets by the defroster door.
T h e te m p e ra tu re o f the outlet air is d ep en d en t o f the
radio o f heated to unheated air (controlled by the
tem perature door).
C O N TR O LS
C-K M odels (Fig. 1A-3)
These controls are m ounted in the center o f the
dash, above the radio assembly. The control incorporates
two levers which m ake use o f bowden cables to control
positioning o f the purge, tem perature and defroster
doors.
Tem perature Lever
This lever control the positioning o f the T E M P E R A ­
T U R E door in the heater distributor assembly. All
incoming "o u tsid e" air is directed a round the heater core
in the C O L D position or through the core in the H O T
position. The desired outlet tem perature is obtained by
blending the heated and unheated air according to the
setting o f the tem perature lever.
Heater-Def Lever
The H E A T E R -D E F lever controls the position o f
the D E F R O S T E R d oor and the P U R G E door. In the
O F F position, the blower is " o n " and incom ing air is
directed up u nder the dash through the p urge door
opening. As the lever is moved to the right o f the O F F
position, the door closes, directing airflow on into the
distributor assembly. W ith the lever at HEATER, the
D E F R O S T E R door directs almost all airflow to the
heater (floor) outlets - a small a m o u n t o f air is directed
to the defroster (dash) outlets. In the D E F 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 h an d side
o f the control assembly. The blower m otor will operate
as soon as the ignition switch is turned to the R U N
position. The control has three' positions only; LO, MED,
HI. There is no O F F position.
G M odels (Fig. 1A -4)
The controls are located in the instrum ent panel,
ju st to the right o f the instrum ent cluster. In opeation,
two levers control all heating operations.
Fig. lA -3 ~ H e a te r C ontrol -C-K Models
Fig. 1A-4- Heater C o n tro l-G Models