Main Units Of The System - Chevrolet 1977 light duty truck Service Manual

the only thing that expanded the refrigerant from a
liquid to a v apor in the first place, removal of that same
h e a t will let the vapor condense into a liquid again. Then
we can return the liquid refrig erant to the evaporator to
be used over again.
Actually, the vapor com ing out of the evaporator is
very cold. We know the liquid refrigerant boils at
tem peratures considerably below freezing and that the
vapors arising from it are only a shade w arm er even
though they do contain quantities o f heat. Consequently,
we c a n 't expect to remove heat from sub-freezing vapors
by "cooling" them in air tem peratures that usually range
between 15 C and 38 C (60 °F and 100 °F)...heat refuses
to flow from a cold object toward a w arm er object.
But with a pump, we can squeeze the heat-laden
v apor into a smaller space. And, when we compress the
vapor, we also concentrate the heat it contains. In this
way, we can make the vap or hotter without adding any
heat. T hen we can cool it in comparatively w arm air.
T h a t is the only responsibility o f a compressor in an
air conditioning system. It is not intended to be a pump
just for circulating the referigerant. Rather, its jo b is to
exert pressure for two reasons. Pressure makes the vapor
hot enough to cool off in w arm air. At the same time, the
compressor raises the re f rig e r a n t's pressure above the
condensing point at the tem perature o f the surrounding
air so it will condense.
As the refrigeran t leaves the compressor, it is still a
v a p o r although it is not quite hot and ready to give up
the heat that it absorbed in the evaporator. One o f the
easiest ways to help refrigerant vapor discharge its heat
is to send it through a readiator-like com ponent known
as a condenser.
The condenser really is a very simple device having
no moving parts. It does exactly the same jo b as the
fam iliar radiator in a
system. There, the steam is nothing more than water
vapor. In passing through the radiator, the steam gives
up its heat and condenses back into water.
The purpose o f the condenser, as the nam e implies,
is to condense the high pressure, high temperature
refrigeran t vapor discharged by the compressor into a
high pressure liquid refrigerant. This occurs when the
high pressure, high tem perature refrigerant is subjected
to the considerably cooler
condenser. This is due to the fu ndam ental laws, which
state that " h e a t travels from the w arm er to the cooler
surface," an d that "when heat is removed from vapor,
liquid is produced."
W hen the refrigerant condenses into a liquid, it
again is ready for boiling in the evaporator. So, we run a
pipe from the condenser back to the evaporator.

MAIN UNITS OF THE SYSTEM

T hese three units
compressor, and the condenser...are the main working
parts in any typical air conditioning system. We have the
evapo rator w here the refrigerant boils and changes into
a vapor, ab sorbing heat as it does so. We have the pum p
or compressor to put pressure on the refrig erant so it can
get rid o f its heat. And we have a condenser outside the
typical home steam -heating
metal surfaces o f
then; the e v a pora tor,
car body to help discharge the heat into the surrounding
air.
Now let's look at the compressor in detail, and some
o f the components that work with these m ain units to
complete the air conditioning system.
AXIAL SIX-CYLINDER CO M PRESSO R
The prim e purpose o f the compressor (fig. IB-4) is
to take the low pressure refrigerant vapor produced by
the evaporator and compress it into a high pressure, high
tem perature vapor which
condenser.
It utilizes the principle that "when a vapor is
compressed, both
raised" which we have already discussed. The axial six
cylinder compressor is mounted above the engine in a
special ru b b e r mounted bracket and is belt driven from
the engine through an electromagnetic clutch pulley on
the compressor.
The compressor has three double-acting pistons,
making it a six cylinder compressor. The compressor has
a l .5 inch bore and 1.1875 inch stroke, giving it a total
displacement of
compressor is by model and serial n um b e r stamped on a
plate on top of the compressor.
Clutch-Pulley
The movable part o f the clutch drive plate is in
front of the pulley and bearing assembly. The arm ature
plate, the movable m ember, is attached to the drive hub
through driver springs and is riveted to both members.
The hub o f the drive plate is pressed over a square drive
key located in the compressor shaft. A spacer and
retainer ring are
assembly is held in place with a self-locking nut. The
pulley rim, power element ring and pulley hub are
formed into a final assembly by molding a frictional
material between the rim and the hub with the power
element ring im bedded in the forward face of the
assembly.
A two-row ball bearing is pressed into the pulley
hub and held in place by a retainer ring. The entire
pulley and bearing assembly is then pressed over the
front head o f the compressor and secured by a retainer
the
ring.
Clutch coil
The coil is molded into the coil housing with a filled
epoxy resin and
assembly. Three protrusions on the rear o f the housing
fit into alignm ent holes in the compressor front head. A
retainer ring secures the coil and housing in place. The
coil has 3.85 ohms resistance at 26.7X1 (80 °F) am bient
tem perature and will require no more than 3.2 amperes
the
at 12 vols D.C. Since the clutch coil is not grounded
internally, a ground lead is required as well as a "h o t"
lead.
Compressor Connector
Compressor connectors, are attached to the compres­
sor rear head by means o f a single bolt and lock washer.
will be sent on
its pressure and tem perature
12.6 cu. in. Identification
assembled to the shaft
must be replaced as a complete
to the
are
o f the
and the