Overhead Systems (C-K-G Models); Motor Home Chassis System; C60 System (G Models) - Chevrolet Light Duty Truck 1978 Service Manual

operation 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, it receives maximum cooling if the air
conditioning controls are calling for cooling. After leaving
the evaporator, the air enters the Heater and Air
Conditioner Selector Duct Assembly where, by means of
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. When, during cooling operations, the air is cooled
by the evaporator to below comfort level, it is then warmed
by the heater to the desired temperature. During "heating
only" operations, the evaporator will not be in operation and
ambient air will be warmed to the desired level in the same
manner.
CK Series
The dash outlets are rectangular in design. The outlets
can be rotated horizontally or vertically to direct air as
desired. Under the left distributor duct is located a floor
cooler which can be rotated to provide cooling air or shut
off completely.
G-Van
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 maximum heating) and is then directed into the
passenger compartment through the heater and/or 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 (G Models)-they do not operate independently.
NOTE: Overhead 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 compartment 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 OTOR HOME CHASSIS SYSTEM
This system performs the cooling functions only. When
heating (above ambient temperatures) is desired, the vehicle
heater must be used. When air conditioning is desired, the
heater should be completely shut off.
This self-contained unit is bracket mounted to the dash
by the body manufacturer.
(recirculated) air only. Air is drawn into the unit, passed
through the evaporator core (receiving maximum 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 temperature
It operates on inside
as it leaves the evaporator core.
Receiver-Dehydrator (Motor Home Chassis
Models)
The receiver-dehydrator, serving as a reservoir for
storage of high pressure liquid produced in the condenser,
incorporates a screen sack filled with the dehydrating agent.
The receiver-dehydrator, used primarily as a liquid
storage tank, also functions to trap minute quantities of
moisture and foreign material which may have remained in
the system after installation or service operations. A
refrigerant sight glass is bult into the receiver-dehydrator
to be used as a quick check of the state and condition of
charge of the entire system. The receiver-dehydrator is
mounted near the condenser.
Sight Glass (M otor Home Chassis Models)
While having no real function to perform in the system,
the sight glass is a valuable aid in determining whether or
not the refrigerant charge is sufficient and for eliminating
some guess work in diagnosing difficulties. The sight glass,
is built into the receiver-dehydrator outlet connection and
is designed and located so that a shortage of refrigerant at
this point will be indicated by the appearance of bubbles
beneath the glass. The dust cap provided should be kept in
place when the sight glass is not in use.
Thermostatic Expansion Valve (Fig. 1B-2)
C-K Overhead, G C60 and Overhead and Motor Home
Chassis systems use a thermostatic expansion valve in place
of a float system.
The valve consists primarily of the power element,
body, actuating pins, seat and orifice. At the high pressure
liquid inlet, is a fine mesh screen which prevents dirt, filings
or other foreign matter from entering the valve orifice.
When the valve is connected in the system, high
pressure liquid refrigerant enters the valve through the
screen from the receiver-dehydrator or condenser and