GMC 4000 Series Service Manual page 77

Sec. 1
Page 70
AIR CONDITIONING
COOLING SYSTEM
This system consists of three major compon­
ents located at the cowl and dash assembly. These
components are described as follows:
1. The evaporator, located under right side
of dash in an enclosed housing assembly, is de­
signed to cool, dry, and clean the air that enters
the cab. Refrigerant enters the evaporator as a
low-pressure mixture of liquid and vapor. The
liquid vaporizes at this low pressure, absorbing
large quantities of heat from air that is forced
through the evaporator core fins. Thus, air direc­
ted into the cab from the evaporator will be cooled
(fig. 1). Also, moisture in air that p asses through
the evaporator condenses on fins and is drained off
carrying away dust and pollen.
2. The refrigerant expansion valve, located
below evaporator core in enclosed dash housing
assembly, regulates the flow of liquid refrigerant
into the evaporator automatically in accordance
DESCRIPTION OF CONTROLS (Figs. 1 and 2)
1. The "AIR CONDITION" lever, when moved
to the extreme right "ON" position, energizes the
com pressor circuit for refrigerant flow in system .
This results in cooling of air directed through
evaporator core.
2. The "DEFROST" lever controls air flow to
the windshield defroster ducts. When the lever is
moved to the extreme right "ON" position, max­
imum air flow is diverted to the windshield de­
froster ducts.
3. The "TEMP" lever directs air flowthrough
either the heater core, the evaporator core, or
through both. Lever may be set at any position
Figure 2 — A ir C ond ition ing Control Switches
G M C S E R V I C E M A N U A L
with requirements of evaporator.
signed to maintain the evaporator pressure suf­
ficiently high to avoid freezing of moisture on
evaporator core and at the same time, provide
maximum cooling efficiency.
of enclosed dash housing assembly and is a cc ess­
ible after opening the dash compartment door.
AIR CIRCULATION SYSTEM
core and heater core results from the use of a
m ulti-speed blower and motor assembly mounted
at side of dash unit (fig. 1). Motor speed is con­
trolled by a fan switch located on instrument panel
(fig. 2).
air conditioning components is given later in this
section.
OPERATING
INSTRUCTIONS
between "COOL" and "HOT" to control temper­
ature of air circulated through cab.
culated and outside air through system . With lever
in extreme left position, system operates entirely
on recirculated air. Intermediate positions of lever
will result in proportional amounts of outside and
recirculated air flow through system .
speed blower motor. Switch has four positions:
Off, Low Speed, Medium Speed, and High Speed.
(fig. 1) can be controlled by positioning of outlet
inner deflector. The inner deflector can also be
oscillated to completely close the outlet if desired.
To close off any one of the outlets will increase
the flow from remaining open outlets. The small
outlet door at base of distributor duct can be open­
ed if desired by pulling downward on door tab.
OPERATING AIR CONDITIONING SYSTEM
lever is in the "OFF" position to reduce electrical
load on battery when starting engine.
TION" control lever to "ON" position. Blower
motor will automatically operate at low speed.
extreme left position.
then select desired blower speed.
switch to high speed position and open windows
for a few minutes to expel warm air from cab.
3. The suction throttling valve (S.T.V.) is de­
The suction throttling valve is mounted at top
The air flow forced through the evaporator
NOTE: A thorough technical description of all
4. The "AIR" lever controls amount of recir­
5. The "FAN SWITCH" controls the three-
6. Direction of air flow from dash outlets
IMPORTANT: Be sure "AIR CONDITION"
1. With engine running, move "AIR CONDI­
2. Move "TEMP" and "DEFROST" levers to
3. Move "AIR" control lever to "A/C" and
For increased cooling, place blower control