Chevrolet 1977 light duty truck, Service Manual

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used on a vehicle with a six cylinder engine.
T h e compressor is m ounted to the engine by
m o u n tin g brackets (Fig. IB-6) an d is belt driven by the
engine w hen the electrom agnetic clutch assembly on the
compressor is energized by the air conditioning controls.
T he purpose o f the com pressor is to pu m p low
pressure, low tem perature r e frig e ran t v apor produced by
the ev a p o ra to r and compress it into a high pressure, high
tem p eratu re vap o r which can then be readily condensed
back to a liquid state by the condenser.
The com pressor has a displacem ent o f 10.0 cu. in.
The compressor has variations in the pulley rim
d ia m e te r specified for the respective vehicle applications.
The basic com pressor m echanism is a modified
scotch yoke with four cylinders located radially in the
sam e plane. Opposed pistons are pressed into a yoke
which rides upon a slider block located on the shaft
eccentric. R otation o f the sh aft provides reciprocating
piston m otion with no "co n n ectin g rods". The m ech a­
nism is com pletely balanced with counterweights. Needle
bearings are used for the sh aft journals and the shaft
eccentric. Pistons and yokes, along with the m ain
cylinder housing an d fro n t cover, are m ade from
alu m in u m to provide light weight. Teflon piston rings
are used to provide both a gas compression seal and
piston-to-bore b e a rin g surface. The outer shell is a
sim ple steel band which encloses a large an n u la r
discharge muffler space.
Two O-rings provide a seal between the compressor
shell and the compressor cylinder. A ru b b e r seal ring
seals the fro n t h e a d to the cylinder assembly and the
sh a ft seal assembly provides a front head to sh aft seal.
R e frig e ra n t flows into the crankcase from the
connector block at the rear, is draw n through the reeds
attached to the piston top d u rin g the suction stroke, and
is discharged outw ard through the discharge valve plate
w hich is held in place at the top o f the cylinder by a
snap ring. D ischarge gas flows out o f the compressor
muffler cavity through the connector block at the rear.
Clutch Coil
The clutch coil is molded into the steel coil housing
a n d must be replaced as a complete assembly. Three
protrusions on the rear o f the housing fit into alignm ent
holes in the compressor fro n t head. The coil is secured to
the fro n t h e a d by a pressed fit between the coil housing
an d neck p ortion o f the fro n t head. T he coil has 3.65
o hm s resistance at 26.1X1 (80 °F) am b ie n t and will
require no m ore th an 3.2 am p eres at 12 volts D.C. The
clutch coil has two terminals for the power and ground
leads.
C lutch-Pulley
T he m ovable part o f the clutch drive plate is in
f ro n t o f an d adjacent to the rotor and bearing assembly.
T h e a rm a tu re plate, the m ovable m em ber, is attached to
the drive h u b through driver springs riveted to both
m em bers. T h e h u b o f the drive plate is pressed on the
com pressor s h a ft and keyed to the shaft by a square
drive key. A self-locking n u t threads on the end o f the
shaft and is tightened against the shaft. T he rotor and
hub is a welded assembly and contains six threaded holes
for m ounting the pulley rim. The pulley rim is secured to
the re a r portion o f the rotor by six screws and six special
lock washers.
A two-row ball bearing is pressed into the rotor hub
and held in place by three punch stakes, 1200 apart, into
the rotor hub n ear the hub bore. T he entire clutch coil,
pulley rim, rotor an d bearing assembly is pressed on the
front head o f the compressor and secured by a retainer
ring.
W hen power is supplied to the clutch coil the
arm atu re plate o f the drive plate and h u b assembly
electromagnetically engages the slotted portion o f the
rotor face which then drives the cran k sh aft through the
drive plate leaf springs and hub.
R efrigerant Lines
Special refrig eran t hose lines are required to carry
the re frig e ran t liquid and vap o r between the various
system components. The hose line with the smallest
d iam eter is called the high pressure liquid line. It is
routed from the condenser or receiver-dehydrator to the
evaporator or thermostatic expansion valve. The large
diam eter hose line connecting the compressor and
evaporator (or accumulator) is the low pressure vapor
line. The large d iam eter hose between the compressor
and condenser is the high pressure v apor discharge line.
These hoses are constructed with a synthetic
m aterial core covered by a woven fabric and coated for
extra protection. This hose is so constructed to withstand
the extreme pressures and te m peratures found in the
m odern refrigeration system.
N one but special refrig er­
ant type hoses should be used.
All systems m ake use o f swaged type connections
(hose to metal fittings) with metal to metai fittings being
m ade using " O " rings. Care must be taken w hen making
these connections that they not be turned down too
tightly or d am ag e to the " O " rings m ay result.
Flexible re frig eran t hoses should not be permitted
to contact the hot engine m anifold nor should they be
bent into a radius o f less than 4 times their diameter.
M uffler
A muffler, located in the high pressure line fro m the
compressor to the condenser, serves as a surge c h am b er
for high pressure gas to reduce the noise level o f the
system while in operation. The muffler is actually a
welded portion o f the compressor connector assembly. It
is found on all truck air contiioning systems.
Fan Slip Clutch
A special engine fan is used on most systems. It is a
19.5 inch six or seven bladed fan, limited by means o f a
viscous clutch to a m axim um speed o f 3400-3700 rpm,
regardless o f the speed o f the engine. The silicone fluid
in the clutch transm its only enough torque to drive the
fan at this limited speed, thus avoiding excessive noise