GMC 1982 Light Duty Truck, Service Manual, Page: 46 / 1435

AIR CONDITIONING IB-3
Fig. 1 B-2-Expansion Valve
the air passes th ro u g h the ev ap o rato r core, it receives
m axim um 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 h e a te r core in the proportions necessary to
provide the desired outlet tem perature. Then conditioned air
enters the vehicle through either the floor distributor duct or
the dash outlets. During cooling operations, the air is cooled
by the evaporator to below comfort level, it is then warmed
by the heater to the desired tem perature. During "heating
only" operations, the evaporator will not be in operation and
am bient air will be warmed to the desired level in the same
manner
AIR DISTRIBUTIO N OUTLETS
C-K 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 -V a n
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 h eater-d efro st modes, the air conditioning
outside air door is closed. The heater air door is open and
outside air is allowed to pass th ro u g h the heater core
(receiving maxim um heating) and is then directed into the
passenger com partm ent through the heater a n d /o r defroster
outlets.
O V E R H E A D SYSTEMS (C-K & G SERIES)
These systems (C69 on C-K & G Series) operate in
conjunction with the C60 S y s t e m - t h e y do not operate
independently. However, control of rear blower motor speed
is possible even when the front system is O FF, thus, rear air
circulation without the refrigerant function may be had by
operating the rear blower control switch.
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 T O R H O M E CHASSIS SYSTEM
This system performs the cooling functions only. When
heating (above am bient 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 m a n u fa c tu re r. It operates on inside
(recirculated) air only. Air is drawn into the unit, passed
through the evaporator core (receiving maxim um cooling)
and then d irected into the vehicle th ro u g h a d ju stab le
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.
System Com ponents
R eceiver-D eh yd rator (M oto r H om e Chassis
M odels)
T he 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 afte r installation or service operations. A
refrigerant sight glass is built 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 H om e Chassis M odels O nly)
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 th at 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.
Therm ostatic Expansion V a lv e (Fig. IB -2 )
C-K and G 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 m atter from entering the valve orifice.
W hen the valve is connected in the system, high
pressure liquid refrigerant enters the valve through the
screen from the receiver-dehydrator or condenser and passes
on to the seat and orifice. Upon passing through the orifice
the high pressure liquid becomes low pressure liquid. The
low pressure liquid leaves the valve and flows into the