General Description; Four-Season System (C-K M Odels; C60 System (G M Odels; Overhead Systems (C-K-G Models) - Chevrolet 1977 light duty truck Service Manual

FOUR-SEASON SYSTEM (C-K MODELS)
Both the h e a tin g
perform ed by this system. Air e ntering the vehicle must
pass through the cooling unit (evaporator) and through
(or around) the heating unit, in that order, and the
system is thus referred to as a " r e h e a t" system.
The evap orator provides m aximum cooling o f the
air passing through the core when the air conditioning
system is calling for cooling. A thermostatic switch,
located on the blow er-evaporator case, acts to control
compressor op eration by sensing the evaporator inlet
line temperature.
System operation is as follows" Air, either outside
air or recirculated air, enters the system and is forced
through the system by the blower. As the air passes
through the evaporator core,
cooling if the air conditioning controls are calling for
cooling. A fter leaving the evaporator, the air enters the
H eater and Air C onditioner Selector Duct Assembly
where, by m eans o f diverter doors, it is caused to pass
through or to bypass the heater core in the proportions
necessary to provide the desired outlet temperature.
Conditioned air then enters the vehicle through either
the floor distributor duct or the dash outlets. W hen,
during cooling operations, the air is cooled by the
evapo rator to below com fort level, it is then warm ed by
the heater to the desired tem perature. D uring "h eating
only" operations, the evaporator will not be in operation
and am bien t air will be w a rm e d to the desired level in
the same m anner.
The dash outlets are rectangular in design. The
outlets can be rotated horizontally or vertically to direct
air as desired. U n de r the left distributor duct is located a
floor cooler which can be rotated to provide cooling air
or shut off completely.
C 6 0 SYSTEM (G M O DELS)
This system perform s both the heating and cooling
functions: however, the h eating and cooling systems
operate independently o f one another — the system
provides e ith er heating or cooling and thus is referred to
as a "p arallel system".
In the air conditioning modes, air (either a mixture
o f inside an d outside at N O R M or inside air only at
MAX) enters the system
evaporator core (receiving m axim um cooling) an d is
then directed into the passenger c om partm ent through
the dash outlets and foot coolers.
A therm ister clipped to the evaporator core is used
to control com pressor
tem perature as it leaves the evaporato r core. As the core
tem peratu re increases the resistance o f the therm ister to
400 ohms, the amplifier (on the control) furnishes
current to energize the compressor clutch coil. As the
eva p o ra to r cools down, the tem perature o f the thermister

GENERAL DESCRIPTION

a n d cooling functions
it receives m axim um
and passes through
o p e r a tio n by sensing
decreases which biases the amplifier off and compressor
clutch coil is de-energized.
are
The dash outlets are rectangular in design and can
be rotated horizontally or vertically to direct air as
desired. Foot coolers are provided on both driver and
passenger side.
In the heater-defrost modes, the air conditioning
outside air door is closed. The heater air door is open
and outside air is allowed to pass through the heater core
(receiving m aximum heating) and is then directed into
the passenger co m p artm en t through the heater a n d /o r
defroster outlets.

OVERHEAD SYSTEMS (C-K-G MODELS)

These systems (C69 on C-K -G Models) operate in
conjunction with the Four-Season System (C-K Models)
or C60 System
independently.
N OTE: O verhead system kits are available for
non-factory installation on C-K Models, providing
the vehicle is equipped with the front system.
These units are self contained, operating on inside
(recirculated) air only. Air is drawn into the unit, passed
through the evaporator core and then directed into the
passenger com partm ent through the air distributor duct.
System control is through the front system. The only
control on the overhead system is a three speed blower
switch.
M O TO R H O M E CHASSIS SYSTEM
This system perform s the cooling functions only.
W hen heating (above am bient temperatures) is desired,
the vehicle heater must be used. W hen air conditioning
is desired, the heater should be completely shut off.
This self-contained unit is bracket m ounted to the
dash by the body m anufacturer. It operates on inside
(recirculated) air only. Air is drawn into the unit, passed
throu gh the e v a p o ra to r
cooling) and then directed into the vehicle through
adjustable outlets.
A thermostatic switch, located on the face plate is
used to control compressor operation by sensing air
tem perature as it leaves the evaporator core.
BASIC A IR C O N D IT IO N E R
the
W hen we look at an air conditioning unit, we will
always find a set o f coils or a finned rad iato r core
through which the air to be cooled passes. This is known
as the "evaporator".
air evaporator. In boiling, or course, the refrigerant absorbs
heat and changes into a vapor. By piping this vapor
outside the car we can bodily carry out the heat that
caused its creation.
Once we get vapor out o f the evaporator, all we
have to do is remove the heat it contains. Since heat is
(G M o d e ls)-th e y do not
core (receiving
The refrigerant boils
operate
m axim um
in the