Chevrolet 1977 light duty truck Service Manual page 54

used on a vehicle with a six cylinder engine.
T he compressor is m ounted
m ounting brackets (Fig. IB-6) an d is belt driven by the
engine w hen the electromagnetic clutch assembly on the
compressor is energized by the air conditioning controls.
The purpose o f the compressor is to pum p low
pressure, low tem perature refrigerant vapor produced by
the evapo rator and compress it into a high pressure, high
tem perature vapor which can then be readily condensed
back to a liquid state by the condenser.
The compressor has a displacement o f 10.0 cu. in.
The compressor has variations
d iam eter specified for the respective vehicle applications.
The basic compressor m echanism is a modified
scotch yoke with four cylinders located radially in the
same plane. Opposed pistons are pressed into a yoke
which rides upon a slider block located on the shaft
eccentric. Rotation o f the shaft provides reciprocating
piston motion with no "connecting rods". The m echa­
nism is completely balanced with counterweights. Needle
bearings are used for the shaft journals and the shaft
eccentric. Pistons and yokes,
cylinder housing an d fro nt cover, are
alum in um to provide light weight. Teflon piston rings
are used to provide both a gas compression seal and
piston-to-bore bearing surface. The outer shell is a
simple steel band which
discharge muffler space.
Two O-rings provide a seal between the compressor
shell and the compressor cylinder. A ru b b er seal ring
seals the front head to the cylinder assembly and the
sh aft seal assembly provides a front head to shaft seal.
R efrigerant flows into
connector block at the rear, is draw n through the reeds
attached to the piston top during the suction stroke, and
is discharged outward through the discharge valve plate
which is held in place at the top o f the cylinder by a
snap ring. D ischarge gas flows out of the compressor
muffler cavity through the connector block at the rear.
Clutch Coil
The clutch coil is molded into the steel coil housing
an d must be replaced as a complete assembly. Three
protrusions on the rear o f the housing fit into alignment
holes in the compressor front head. The coil is secured to
the front h e a d by a pressed fit between the coil housing
and neck portion of the fron t head. The coil has 3.65
ohm s resistance at 26.1X1 (80 °F) am b ient and will
require no m ore than 3.2 am peres at 12 volts D.C. The
clutch coil has two terminals for the power and ground
leads.
C lutch-Pulley
The m ovable part o f the clutch drive plate is in
f ro n t of an d adjacent to the rotor and bearing assembly.
T he arm a tu re plate, the movable m ember, is attached to
the drive hub through driver springs riveted to both
m em bers. The hub of the drive plate is pressed on the
com pressor sh a ft and keyed to the shaft by a square
drive key. A self-locking nut threads on the end o f the
to the engine by
in the pulley rim
along with the m ain
m ade from
encloses a large annu lar
the crankcase from the
shaft and is tightened against the shaft. The rotor and
hub is a welded assembly and contains six threaded holes
for mounting the pulley rim. The pulley rim is secured to
the rear 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 near the hub bore. The entire clutch coil,
pulley rim, rotor and 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 ature plate o f the drive plate and hub assembly
electromagnetically engages the slotted portion o f the
rotor face which then drives the crankshaft through the
drive plate leaf springs and hub.
Refrigerant Lines
Special refrigerant hose lines are required to carry
the refrigerant liquid and vapor between the various
system components. The hose line with the smallest
diam 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
evaporator (or accumulator) is the low pressure vapor
line. The large diam eter hose between the compressor
and condenser is the high pressure vapor discharge line.
These hoses are constructed
material core covered by a woven fabric and coated for
extra protection. This hose is so constructed to withstand
the extreme pressures and temperatures found in the
m odern refrigeration system.
ant type hoses should be used.
All systems make 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 when making
these connections that they not be turned down too
tightly or dam age to the " O " rings m ay result.
Flexible refrigerant hoses should not be permitted
to contact the hot engine manifold 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 from the
compressor to the condenser, serves as a surge cham ber
for high pressure gas to reduce the noise level o f the
system while in operation. The muffler is actually a
welded portion of 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 of the speed o f the engine. The silicone fluid
in the clutch transmits only enough torque to drive the
fan at this limited speed, thus avoiding excessive noise
the compressor and
with a synthetic
None but special refriger­