Chevrolet 70 Series 1970, Service Manual

Page: 128 / 841

CAB AND BODY MOUNTINGS 1-97
AIR CONDITIONING
(INCLUDES HEATING SYSTEM)
Contents of th is se ctio n a re liste d in Index below:
Subject P age No.
G eneral Inform ation ............................................................................... ...... 1-97
O perating Instructions ........................................................................... ...... 1-101
S ystem O p e r a t io n ............................................................................................. 1-103
O n-V eh icle S e r v i c e ........................................................ ................................ 1-117
Insufficient Cooling D iagn osis C h a r t ................................................. ...... 1-140
R efrigerant Line C onnections Torque S p e c i f i c a t i o n s ............... ...... 1-142
A ir Conditioning S p e c if ic a t io n s ............................................................ .......1-142
GENERAL INFORMATION
INTRODUCTION
The cab heating and optional a ir conditioning
s y ste m is an in tegral unit designed to provide
d river com fort by heating or cooling, dehum idify-
ing, and filterin g the a ir circu lated through the cab.
B lo w ers in main sy s te m a ssu r e am ple a ir c ircu ­
lation to a ssu r e com plete driver com fort in both
hot and cold w eather. F igu res 1 and 2 show typical
arrangem ent of s y ste m units in conventional and
alum inum cab m odels.
HEATING SYSTEM
R efer to "ALUMINUM TILT CABS" (SEC. ID)
o r "CONVENTIONAL CABS" (SEC. IB) of this
manual for inform ation on standard heating sy ste m .
CONDENSING SYSTEM (F ig. 3)
T his sy ste m is com p rised of th ree major
com ponents: the c o m p r esso r, the condenser, and
the receiver-d eh yd rator unit.
The s ix -c y lin d e r axial type co m p re sso r is
b elt-d riv en through electrom agn etic p u lley-clu tch
a sse m b ly . The co m p resso r pumps refrigeran t
when the com p resso r clutch co il is energized.
The c o m p resso r with clutch a ssem b ly is
mounted toward front of engine p a r a lle l to the
engine crankshaft.
The condenser is a fin and tube-type co re de­
sig n ed to change high p r e s s u r e refrigeran t vapor
to a liquid due to heat rem oval. The condenser is
mounted in front of engine radiator w here it r e ­
c e iv e s a high volum e of a ir due to veh icle m ove­
ment and engine fan.
The receiv er-d eh y d ra to r, bracket mounted to
right sid e of radiator sh e ll or sh eet m etal, i s de­
sign ed to sto r e liquid refrigeran t and to rem ove
sm a ll tr a c e s of m oisture that may be in sy ste m
after purging and evacuating. A sight g la ss at top
of this component i s used to ob serv e flow of liquid
refrigeran t in sy ste m .
COOLING SYSTEM (F ig. 3)
T his s y s te m c o n s is ts of th ree m ajor compon­
ents; the evaporator c o re , the refrigeran t expan­
sion va lv e, and the P .O .A . (pilot, operated, a b so­
lute) valve, on aluminum tilt m odels, or on con­
ventional m odels (suction throttling valve).
The evaporator c o re , located in sid e main
heater housing, w orks in conjunction with the heat­
er core to provide conditioned a ir entering cab
(se e fig s . 4 and 5). R efrigerant en ters the evapor­
ator a s a lo w -p r e ssu r e m ixture of liquid and vapor.
The liquid vap orizes at th is low p r e s s u r e , absorb­
ing la rg e quantities of heat from a ir that i s forced
through the evaporator core fin s. Thus, a ir d irect­
ed into the cab from the evaporator w ill be cooled
(figs. 4 and 5). A lso , m oistu re in air that p a s s e s
through the evaporator condenses on fin s and is
drained off carrying away dust and pollen.
The refrigeran t expansion valve, located b e ­
hind main h eater housing in the liquid lin e of the
evaporator in let or below evaporator c o il, auto­
m atically regu lates the flow of liquid refrigeran t
into the evaporator core.
The P .O .A . valve, mounted b esid e m ain heater
housing, and attached to outlet lin e of evaporator
(on aluminum "tilt cab m odels) i s herm etically
se a le d and is rep laceab le only a s an a ssem b ly .
The P.O .A . valve i s designed to prevent w ater
condensate from freezin g on the evaporator core
and p rovid es m axim um cooling efficien cy by m ain­
taining a predeterm ined minimum refrigeran t
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCKSHOP MANUAL