service OPEL 1900 1973 Service Manual

98-20 1973 OPEL SERVICE MANUAL
If we were to put a thermometer in the cold drain
water, we would see the temperature gradually creep
upwards. That is to be expected because heat is flow-
ing into the cold water making it warmer. Before
long the water would be as warm as the stored foods.
Then the water could no longer attract heat because
heat will not flow from one warm object to another
equally warm object. Since we no longer can draw
heat out of the foods we no longer are cooling them.
Now, let’s see what happens when we put ice instead
of cold water into the ice-box. This time, we’ll set the
thermometer on top of the ice (Fig. 9B-5). When wefirst look at the thermometer, it reads 32 degrees. A
couple of hours later, we open the ice compartment
door. The ice block is smaller because some of the ice
has already melted away
- but the thermometer still
reads 32 degrees. Again, still later, even more of the
ice has melted, yet the termometer continues to read
32 degrees. So long as any ice remains, no matter
how much of it has melted away, the temperature of
the ice stays right at 32 degrees.
All this time the ice has been soaking up heat, yet it
never gets any warmer no matter how much heat it
draws from the stored food. On the other hand, the
cold drain water got progressively warmer as it
soaked up heat. Why is it the addition of heat will
make water warmer yet won’t raise the temperature
of ice above the 32 degrees mark? If we till one
drinking glass with ice and another with cold water,
and put both glasses in the same room where they
could absorb equal amounts of heat from the room
air, we will find it takes much, much longer for the
ice to melt and reach room temperature than it did
for the water in the other glass to reach the same
temperature. Obviously, most of the heat was being
used to melt the ice. But it was the heat that appar-
ently disappeared or went into hiding because if
couldn’t be located with a thermometer. To best de-
scribe this disappearing heat, scientists turned to
Latin for the right word. They chose the word “la-
tent” which means hidden.
Latent Heat
So latent heat is nothing more nor less than hidden
heat which can’t be found with a thermometer.
What happens to the latent heat? Where does it
disappear to? At first it was thought it was in the
water that melted from the ice. But that wasn’t ex-
actly the right answer because, upon checking water
temperature as it melts from ice, it will be found that
it is only a shade warmer than the ice itself. It is not
nearly warm enough to account for all the heat the
ice had absorbed. The only possible answer is that
the latent heat had been used up to change the ice
from a solid into a liquid.
Many substances can be either a solid, or a liquid, ora gas. It just depends on the temperature whether
water for example was a liquid, or a solid (ice), or gas
(steam) (Fig.
9B-6).Figure 99-6 Temperature Determines State of Water
If we put some water in a tea-kettle, set it over a tire
and watch the thermometer as the water gets hotter
and hotter, the mercury will keep rising until the
water starts to boil. Then the mercury seems to stick
at the 212 degrees mark. If we put more wood on the
fire, despite all the increased heat, the mercury will
not budge above the 212 degree mark (Fig.
9B-7).Figure 98.7 Boiling Water Never Exceeds 2 12
DegreesEven though many housewives won’t believe it, no
matter how large or hot you make the flame, you
can’t make water hotter than 2 12 degrees. As a liquid
changes into a gas, it absorbs abnormally great
amounts of heat without getting any hotter. Here is
another instance where heat disappears.
Now we have two different kinds of latent heat,
which are quite alike. To keep their identities sepa-
rate, the first one is called latent heat of fusion. Since
fusion means the same as melting, it is a good de-
scriptive name. The other kind is called latent heat
of vaporization because‘ that means the same as
evaporation.
It may seem as though we have drifted into a story

9B-22 1973 OPEL SERVICE MANUAL
We can change a vapor back into a liquid by chilling
it, or do the same thing with pressure. When we
condense a vapor we will find that the heat removed
just exactly equals the amount of heat that was neces-
sary to make the substance vaporize in the first place.
At last the lost is found! The latent heat of vaporiza-
tion the heat that apparently disappeared when
a liquid boiled into a vapor again reappears on
the scene when that same vapor reverts back into a
liquid. It is just like putting air into a balloon to
expand it and then letting the same amount of air out
again to return the balloon to its original condition.
We know that any substance will condense at the
same temperature at which it boiled. This tempera-
ture point is a clear-cut division like a fence. On one
side, a substance is a liquid. Immediately on the
other side it is a vapor. Whichever way a substance
would go, from hot to cold or cold to hot, it will
change its character the moment it crosses over thefence.But pressure moves the fence! Water will boil at 212
degrees under normal conditions. Naturally, we ex-
pect steam to condense at the same temperature. But
whenever we put pressure on steam, it doesn’t! It will
condense at some temperature higher than 212 de-
grees. The greater the pressure, the higher the boiling
point and the temperature at which a vapor will
condense. This is the reason why pressure cookers
cook food faster, since the pressure on the water
permits it to boil out at a higher temperature. We
know that R-12 boils at 21.7 degrees below zero. A
thermometer will show us that the rising vapors,
even though they have soaked up lots of heat, are
only slightly warmer. But the vapors must be made
warmer than the room air if we expect heat to flow
out of them. Also, the condensing point temperature
must be above that of room air or else the vapors
won’t condense.This is where pressure comes to the rescue. With
pressure, we can compress the vapor, thereby con-
centrating the heat it contains. When we concentrate
heat in a vapor that way, we increase the intensity of
the heat or, in other words, we increase the tempera-ture;because temperature is merely a measurement
of heat intensity. And the most amazing part of it all
is that we’ve made the vapor hotter without actually
adding any additional quantity of heat (Fig.
9B-12).
Use of Pressure in RefrigerationBecause we must live by press&s and gauges in air
conditioning work, the following points are men-
tioned so that we will all be talking about the same
thing when we speak of pressures.
All pressure, regardless of how it is produced, is
measured in pounds per square inch (psi).Figure 98.12 Compressing a Vapor Concentrates its
HeatAtmospheric Pressure is pressure exerted in every
direction by the weight of the atmosphere. At higher
altitudes air is raritied and has less weight. At sea
level atmospheric pressure is 14.7 psi.
Any pressure less than atmospheric is known as a
partial vacuum or commonly called a vacuum. A
perfect vacuum or region of no pressure has never
been mechanically produced. Gauge pressure is used
in refrigeration work. Gauges are calibrated in
pounds (psi) of pressure and inches of Mercury for
vacuum. At sea level
“0” lbs. gauge pressure is
equivalent to 14.7 lbs. atmospheric pressure. Pres-
sure greater than atmospheric is measured in pounds
(psi) and pressure below atmospheric is measured in
inches of vacuum. The “0” on the gauge will always
correspond to the surrounding atmospheric pressure,
regardless of the elevation where the gauge is being
used.
Basic Refrigerator OperationWe’ve now covered all the ground-rules that apply to
refrigeration. Most likely they still are a little hazy,
but it is easy enough to remember these main points.
All liquids soak up lots of heat without getting any
warmer when they boil into a vapor, and, we can use
pressure to make the vapor condense back into a
liquid so it can be used over again. With just that
amount of knowledge, here is how we can build a
refrigerator.
We can place a flask of refrigerant in an ice-box. We
know it will boil at a very cold temperature and will
draw heat away from everything inside the cabinet
(Fig. 9B-13).
We can pipe the rising vapors outside the cabinet and
thus provide a way for carrying the heat out. Once

9B-24 1973 OPEL SERVICE MANUAL
Figure 9B-15 Compressor Assembly - GT Shown
Figure 3B-16 Condenser Assembly
condenser. The refrigerant vapor gives up its heat,
which is quickly and easily radiated into the sur-
rounding air through the large finned surfaces of the
condenser. In giving up its heat, the refrigerant vapor
condenses back into liquid which collects in a pool
at the bottom of the condenser.
As we have said before, when the refrigerant con-
denses into a liquid, it again is ready for boiling in the
evaporator. So, we can run a pipe from the condenser
back to the evaporator.
Main Units of the SystemThese three units then; the evaporator, the compres-
sor, and the condenser are the main working
parts of any typical air conditioning system. We have
the evaporator where the refrigerant boils andchanges into a vapor, absorbing heat as it does so. We
have the pump or compressor to put pressure on the
refrigerant so it can get rid of its heat. And we have
a condenser outside the car body to help discharge
the heat into the surrounding air.
Pressure and FlowThere is one more unit that co-operates with thesethree. It doesn’t do any real work, but it does act as
sort of a traffic officer in controlling the flow of the
refrigerant through the system. To get a better idea
of what this does. let’s first do a li,ttle exoerimentine
with an ordinary’ tire pump.
When we use a
t,ire pump to Sate an automobile
tire, we are creating pressure only because we are
“pushing” against the air already entrapped inside
the tire. If you question this, just try pumping up a
tire that has a large puncture in it. You could pump
all day, and still not be able to build up any pressure.
As fast as you would pump the air in, it would leak
out through the puncture.
Abou~t all you would be
doing would be circulating nice fresh air through the
tire.
1Jnless you have something lo push against - to
block the tlow of air
- you can’t create more than a
mere semblance of pressure.
The same situation holds true in an air conditioning
system. The compressor can pump refrigerant vapor
through the system, but unless it has something to
push against, it cannot build up pressure. All the
compressor would be doing would be to circulate the
vapor without increasing its
pres,sure.Yet we can’t just block the flow through the system
entirely. All we want to do is put pressure on the
refrigerant vapor so it will condense at normal tem-
peratures. What’s more, this
musi: be done some time
after the vapor leaves the evaporator and before it
returns again as a liquid. We can’t have high pressure
in the evaporator because that would slow down the
boiling of the refrigerant and thus penalize the re-
frigerating effect.
Controlling Pressure and FlowPressure and flow can be controlled with a float
valve, or with a pressure-regulating valve. They do
the same job, but in a different way.
Since the float valve type will give us a better idea of
pressure and flow control, let’s look at it first (Fig.
9B-17).It consists simply of a float that rides on the surface
of the liquid refrigerant. As the refrigerant liquid
boils and passes off as a vapor, naturally the liquid
level drops lower and lower. Correspondingly, the
float, because it rides on the surface of the refriger-
ant, also drops lower and lower as the liquid goes
down.By means of a simple system of mechanical linkage,
the downward movement of the float opens a valve
to let refrigerant in. The incoming liquid raises the
fluid level and, of course, the float rides up with it.
When the surface level of the refrigerant liquid re-
aches a desired height, the float: will have risen far

98-26 1973 OPEL SERVICE MANUAL
greater than the opposing pressure in the power ele-
ment. Therefore, the valve remains closed. When the
compressor is started, it will reduce the pressure and
temperature of the refrigerant in the cooling coil to
a point where the vapor pressure in the power ele-
ment becomes the stronger. The seat then moves off
the orifice and liquid starts to flow through the valve
orifice into the cooling coil.
The purpose of the power element is to help deter-
mine the quantity of liquid that is being metered into
the cooling coil. As the temperature of the low pres-
sure line changes at the bulb, the pressure of
the
vapor in the power element changes, resulting in a
change of the position of the seat. For example, if the
cooling coil gets more liquid than is required, the
temperature of the low pressure line is reduced and
the resultant lowering of the bulb temperature
reduces the pressure of the vapor in the power ele-
ment, allowing the seat to move closer to the orifice.
This immediately reduces the amount of liquid leav-
ing the valve. Under normal operation, the power
element provides accurate control of the quantity of
refrigerant to the cooling coil.
To employ our tire pump analogy once more for
clarity, it is the same situation that would exist if you were inflating a tire with a very slow leak. Providing
you pumped the air into the tire as fast as it leaked
out, you would be able to maintain pressure even
though the air would merely be circulating through the tire and leaking out through the puncture.
To Sum Up
So far, we’ve discussed only what each unit in an air
conditioning system does. We’ve learned that the
evaporator is the unit in which liquid refrigerant
soaks up heat from the air, the compressor is a pump
for squeezing this heat out of the vapor, the con-
denser is a radiator for getting rid of the heat, and the
thermostatic expansion valve is a device for regulat-
ing the pressure on the refrigerant. Now, let’s
find
out how the temperature of the cooled air is con-
trolled.
METHOD OF TEMPERATURE CONTROL
To achieve temperature control, the compressor is
run intermittently, automatically turning on and off
as necessary to maintain proper temperature.
Thermostatic Switch
The compressor can be started and stopped au-
tomatically through the use of an electro-magnetic
clutch and a thermostat affected by variations of temperature.
The job is usually done by a gas bulb thermostat (Fig.
9B-21).
Figure 9B-21 Thermostatic Switch Schematic
With the gas bulb type of thermostat, a highly expan-
sive gas is sealed into a metallic bulb which is located
in the air stream as it leaves the evaporator. A small
tube leads from the bulb to a bellows operated switch. As air temperature rises, the gas inside the
bulb expands, travels through the tube to the bellows
and closes the electrical switch that engages the com-
pressor clutch.
Of course, as soon as the compressor starts running,
the temperature begins to go down. As the air being
cooled gets colder, the gas in the thermostat bulb
begins to reduce the pressure on the switch bellows.
This
Ilips “off’ the switch and disengages the com-
pressor clutch.
REFRIGERANTS
No matter how scientifically refrigerating machinery
is built or how
efftciently it runs, it alone cannot
remove heat. The only thing that carries heat out of
a refrigerator cabinet or an automobile is the sub-
stance we call the refrigerant.
There are many refrigerants known to man. In fact,
any liquid that can boil at temperatures somewhere
near the freezing point of water can be used.
But a boiling point below the temperature at which
ice forms is not the only thing that makes a good
refrigerant. A refrigerant should also be non-
poiso-
nowand non-explosive to be safe. Besides that, we
want a refrigerant that is non-corrosive and one that
will mix with oil.
Since Nature did not provide an ideal refrigerant,
chemists went to work to see if they could do any
better. They did! But it wasn’t as simple as that.
At first, they tried to improve existing natural refrig-
erants. But after exploring innumerable trails along

9B-28 1973 OPEL SERVICE MANUAL
Thus, from the standpoint of comfort, complete air
conditioning should control the relative humidity of
the air as well as its temperature.
By reducing the humidity, we sometimes can be just
as “cool” in a higher room temperature than other-
wise would be comfortable. Laboratory tests have
shown that the average person will feel just as cool
in a temperature of 79 degrees when the relative
humidity is down around 30 percent as he will in a
cooler temperature of 72 degrees with a high relative
humidity of 90 percent.
There are practical limits though within which wemust stay when it comes to juggling humidity. For
human comfort, we can’t go much below a relative
humidity of 30 percent because anything lower than
that would cause an unpleasant and unhealthy dry-
ness in the throat and nasal passages.
Summertime temperatures of 85 degrees sometimes
bring with them relative humidities around 75 to 80
percent. Some coastal cities have relative humidities
averaging as high as 87 percent. To gain maximum
human comfort, an air conditioning system should
cool the air down and reduce the humidity to com-
fortable limits.
The cooling job usually is done just as it is in a
refrigerator. A compressor sends refrigerant through
a chilling unit where it absorbs heat. The heat is
drawn out of the air which circulates through the
chilling unit. Along with the cooling job it does, the
evaporator unit also removes much of the moisture
from the air. Everyone is familiar with the sight of
thick frost on the freezer of a refrigerator. That frost
is simply frozen moisture that has come out of the
air.
Figure 99.22 Condensation
The evaporator unit in an air-conditioning system
does the same thing with this one exception. Becauseits temperature is above the freezing point, the mois-
ture does not collect in the form of ice or frost.
Instead, the moisture remains fluid and drips off the
chilling unit. This action is similar to what occurs on
the cool bathroom mirror when a hot shower is
turned on (Fig. 9B-22). A further advantage of airconditioning is that dust and pollen particles are
trapped by the wet surfaces of
.the evaporator core
and then drained off with the condensed moisture.
This provides very clean, pure air for breathing, and
is of great benefit to those who suffer from asthma
or ahergies such as hay fever.
Basic Refrigeration CycleLet’s review the basic refrigeration cycle. Keep this
basic cycle in mind because knowledge of the cycle,
knowledge of the particular system you are working
on and proper use of the gauges will permit quick,
accurate diagnosis of problems as they arise.
Any refrigeration system takes advantage of the
principles just described. The air conditioning sys-
tem illustrated in Fig. 9B-23 contains
five basic parts;
a compressor, a condenser, a receiver, an expansion
valve and an evaporator. Assuming R-12 as our re-
frigerant, let us follow through the refrigeration cy-
cle.Refrigerant gas under low pressure is drawn into the
compressor where it is compressed to a high pres-
sure. During compression, the refrigerant gas is
heated. When sufficient pressure is built up, the hot
gas passes into the condenser where it cools by giving
off heat to the air passing over the condenser sur-
faces.As the refrigerant gas cools, it condenses into a liquid
at high pressure and accumulates in the receiver. The
high pressure liquid refrigerant passes to the expan-
sion valve at the entrance to the evaporator. At the
valve orifice the pressure is lowered and the refriger-
ant enters the evaporator core as a low pressure liq-
uid. When the refrigerant is exposed to the lower
evaporator pressure, it begins to boil and is changed
to a vapor state. As the refrigerant passes through
the evaporator, it continues to boil by absorbing heat
from the air passing over the evaporator surfaces
until it is completely vaporized. From the evaporator
the cool low pressure refrigerant gas is drawn back
to the compressor and the cycle repeated.
Thus the air passing over the evaporator surfaces is
cooled simply by giving up heat to the refrigerant
during the boiling process.
CHEMICAL INSTABILITY AND REFRIGERATING
SYSTEM FAILURESA sealed refrigerating system is a complex physical-
chemical combination which is designed for stability

9B-30 1973 OPEL SERVICE MANUAL
refrigerant penetrates to every nook and cranny of
the unit.
Among the many desirable properties of R-12, is its
stability under operating conditions. However, while
more stable than the other refrigerants under the
same conditions, it, too, can be caused to form harm-
ful acids which will eventually fail the system.OilOil is the most complex of all of the organic chemi-
cals. Its stability in a refrigerating system is depend-
ent upon the source of crude oil and its method of
refining. A good refrigerating oil must be free of
sludge and gum-forming substances and free of
harmful impurities, such as sulphur. It must also be
stabilized to resist oxidation and must have a high
degree of resistance to carbonization.
The chemical properties of the lubricating oil form
another very important consideration in the chemi-
cal stability within the system. Like the refrigerant,
it travels to every nook and cranny of the unit.
The factory obtains the finest oils which have been
refined from the most desirable
crudes. It is reproc-
essed at the factory before it is charged into a system
or poured into a container for resale. Its
voscosityand flash point are checked and it is forced through
many sheets of filtering paper.
Even the containers in which it is poured for resale
are processed. As you recive it for field service it is
the cleanest, dry&, and purest oil that is humanly
possible to make. Leaving the container uncapped
even for a few minutes allows the oil to absorb mois-
ture from the air. Many system failures have been
caused by chemical reactions which were started by
servicemen adding contaminated oil.
Desiccants (Dehydrating Agent)Over the years the industry has spent hundreds of
thousands of dollars in finding and developing
chemical substances which are suitable for use in
refrigerating systems. An ideal desiccant must have
the following characteristics:
I. High capacity.
2. High eficiency.
3. Low tendency to powder.
4. Absorb moisture without reacting chemically with
it.5. Allow refrigerant to flow through it with mini-
mum restriction.
6. Retain moisture at high temperature.This has been a difficult combination to find. While
some desiccants excel in several of the desirable char-
acteristics, they are unsatisfactor:y in others.
Activated Silica Alumina, used in current
receiver-dehydrators, is a most satisfactory desiccant. How-
ever, its ability to retain moisture is affected by its
temperature. As the temperature increases, its ability
decreases. This means that moisture which is re-
tained at a lower temperature may be put back into
the system at a higher temperature.
MAINTAINING CHEMICAL STABILITY IN THE
REFRIGERATION SYSTEMThe metal internal parts of the refrigeration system
and the refrigerant and oil contained in the system
are designed to remain in a state of chemical stability
as long as pure R-12 plus refrigeration oil is used in
the system. However, when abnormal amounts of
foreign materials, such as dirt, air or moisture are
allowed to enter the system, the chemical stability
may be upset (Fig. 9B-24).
Figure
98.24 System Contaminants
When accelerated by heat, these contaminants may
form acids and sludge and eventually cause the
breakdown of components within the system. In ad-
dition, contaminants may affect the temperature
pressure relationship of R-12, resulting in improper
operating temperature and pressures and decreased
efficiency
OF the system.
The following general practices should be observed
to maintain chemical stability in the system:
Whenever it becomes necessary to disconnect a re-
frigerant or gauge line, it should be immediately
capped. Capping the tubing will also prevent dirt and
foreign matter from entering.
Tools should be kept clean and dry. This also in-
cludes the gauge set and replacement parts.

REFRIGERANT COMPONENTS ALL MODELS9B- 31
When adding oil, the container should be exception-
ally clean and dry due to the fact that the refrigera-
tion oil in the container is as moisture-free as it is
possible to make it. Therefore, it will quickly absorb
any moisture with which it comes in contact. For this
same reason the oil container should not be opened
until ready for use and it should be capped immedi-
ately afte;r use.
When it is necessary to open a system, have every-
thing you will need ready and handy so that as little
time as possible will be required to perform the oper-
ation. Don’t leave the system open any longer than
is necessary.
Finally, after the operation has been completed and
the system sealed again, air and moisture should be
evacuated from the system before recharging.
THE PRIMARY CAUSES OF SYSTEM FAILURES
LeaksA shortage of refrigerant causes oil to be trapped in
the evaporator. Oil may be lost with the refrigerant
at point of leakage. Both of these can cause compres-
sor seizure.
Oil circulates in the system with the refrigerant; in
solution with the liquid and in globules with the
vapor. It leaves the compressor by the action of the
pistons and mixes with the refrigerant liquid in the
condenser. The oil then enters the evaporator with
the liquid and, with the evaporator properly flooded,
is returned to the compressor through the low pres-
sure line. Some of the oil returns as globules in the
vapor, but more important, it is swept as a liquid
along the walls of the tubing by the velocity of the
vapor. If the evaporator is starved, the oil cannot
return in sut?icient quantities to keep the compressor
properly lubricated.
High Temperature and PressureAn increase in temperature causes an increase in
pressure. This accelerates chemical instability due to
existing contaminants in the system, and initiates
chemical instability in clean systems. Other results
are brittle hoses,
“0” ring gaskets, and valve dia-
phragms with possible decomposition, broken com-
pressor discharge reeds, and seized compressor
bearings.
A fundamental law of nature accounts for the fact
that when a substance, such as a refrigerant, is in-
creased in temperature, its pressure is also increased.
Any chemical reactions caused by contaminants al-
ready in the system are greatly accelerated as the
temperature increases. A 15 degree rise in tempera-
ture doubles the chemical action. Even in a goodclean system, heat alone can start a chain of harmful
chemical reactions.
While temperature alone can cause the synthetic rub-
ber parts to become brittle and possibly to decom-
pose, the increased pressure can cause them to
rupture or blow.
As the temperature and pressure increases the stress
and strain on the compressor discharge reeds also
increases. This can result in broken reeds. Due to the
effect of the contaminants caused by high tempera-
ture and pressure, compressor bearings can be
caused to seize.
High temperature and pressure are also caused by air
in the system.
Air in the SYstemAir results from a discharged system or careless ser-
vicing procedures. This reduces system capacity and
efficiency and causes oxidation of oil into gum and
varnish.
When a leak causes the system to become dis-
charged, the resulting vacuum within the system will
cause air to be drawn in. Air in the system is a
non-condensable gas and will build up in the con-
denser as it would in an air compressor tank. The
resultant heat produced will contribute to the condi-
tions discussed previously.
Many systems are contaminated and also reduced in
capacity and efficiency by servicemen who either do
not know or are careless regarding proper servicing
procedures.
Too frequently, systems which have been open to the
atmosphere during service operations have not been
properly purged or evacuated. Air is also introduced
into the system by unpurged gauge and charging
lines. Remember that any air in the system is too
much air.
Poor ConnectionsHose clamp type fittings must be properly made.
Hoses should be installed over the sealing flanges and
with the end of the hose at the stop flange. The hose
should never extend beyond the stop flange. Locate
the clamp properly and torque as recommended. Be
especially careful that the sealing flanges are not
nicked or scored or a future leak will result.
When compression fittings are used, over tightening
can cause physical damage to the “0” ring gasket
and will result in leaks. The use of torque and back-
ing wrenches is highly recommended. When making
a connection with compression fittings, the gaskets
should always be first placed over the tube before

98-32 1973 OPEL SERVICE MANUAL
inserting it in the connection. Another precaution -inspect the fitting for burrs which can cut the
“0”ring.
Restrictions
Restrictions may be due to powdered desiccant or
dirt and foreign matter. This may result in starved
evaporator and loss of cooling, or a seized compres-
SOT.When the amount of moisture in a system sufti-
ciently exceeds the capacity of the desiccant, it can
break down the desiccant and cause it to powder.
The powder passes through the dehydrator screen
with the refrigerant liquid and is carried to the ex-
pansion valve screen. While some of it may pass
through the valve screen into the evaporator, it may
quickly build up to cause a restriction.
Due to the fact that sufftcient oil can not be returned
to the compressor, it may seize.
Dirt
Dirt, which is any foreign material, may come from
cleaner residues, cutting, machining, or preserving
oils, metal dust or chips, lint or dust, loose rust,
soldering or brazing fluxes, paint or loose oxide
scale. These can also cause seized bearings by abra-
sion or wedging, discharge and expansion valve fail-
ure, decomposition of refrigerant and oil, or
corrosion of metal parts.
CorrosionCorrosion and its by-products can restrict valve and
drier screens, rough bearing surfaces or rapid fatigu-
ing of discharge reeds. This can result in high tem-
perature and pressure, decomposition or leaks. In
any event, this means a wrecked compressor.
From this, we can see the vicious circle that can be
produced in a refrigerating system to cause its fail-
ure. Corrosion can be the indirect cause of leaks, and
leaks can be the direct cause of corrosion. We can
also see the important role we as servicemen play in
maintaining chemical stability.
The major cause of corrosion is moisture.
Moisture
Moisture is the greatest enemy of refrigerating sys-
tems. Combined with metal, it produces oxide, Iron
Hydroxide and Aluminum Hydroxide. Combined
with R-12 it produces Carbonic acid, Hydrochloric
acid, and Hydrofluoric acid. Moisture can also cause
freeze-up of expansion valve and powdered desic-
cant.Although high temperature and dirt are responsible
for many difficulties in refrigerating systems, in most
instances it is the presence of moisture in the system
that accelerates these conditions. It can be said,themfore, that moisture is the greatest enemy of all.
The acids that it produces, in combination with both
the metals and the refrigerant, cause damaging
COT-
rosion. While the corrosion may not form as rapidly
with R-12 as with some other refrigerants, the even-
tual formation is as damaging.
If the operating pressure and temperature in the
evaporator is reduced to the freezing point, moisture
in the refrigerant can collect at the orifice of the
expansion valve and freeze. This temporarily re-
stricts the flow of liquid causing erratic cooling.
As previously mentioned, moisture in excess of the
desiccant’s capacity can cause it to powder.
YOU SHOULD KNOW AND REMEMBER..That the inside of the refrigerat,ion system is com-
pletely sealed from the outside world. And if that
seal remains broken at any point
- the system will
soon be destroyed. That complete and positive seal-
ing of the entire system is vitally important and that
this sealed condition is absolutely necessary to retain
the chemicals and keep them in a pure and proper
condition.
That all parts of the refrigeration system are under
pressure at all times, whether operating or idle, and
that any leakage. points are continuously losing re-
frigerant and oil.
That the leakage of refrigerant can be so silent that
the complete charge may be lost without warning.
That refrigerant gas is heavier than air and will rap-
idly drop to the floor as it flows from a point of
leakage.
That the pressure in the system may momentarily
become as high as 400 lbs. per square inch, and that
under such pressure the molecules of refrigerant are
forced out through the smallest opening or pore.
That the compressor is continually giving up some
lubricating oil to the circulating refrigerant and de-
pends upon oil in the returning refrigerant for con-
tinuous replenishment. Any stoppage or major loss
of refrigerant will therefore be fatal to the compres-
SOT.That the extreme internal dryness of a properly proc-
essed system is a truly desert condition, with the
drying material in the receiver holding tightly on to
the tiny droplets of residual moisture.

98-34 1973 OPEL 3ERVlCE MANUAL
9B-23Figure
98.26 Compressor Front and Rear Heads
and circulated through the system via a 3/16 inch
diameter oil passage through the shaft center and
also four 5/64 inch diameter holes drilled perpen-
dicular to the shaft. The inner rotor is driven by the
shaft.TUBE
Figure
98-27 Compressor Oil Flow
4. Shaft and
Gash Plate Assembly - The shaft andwash plate assembly (see Figure 9B-162) consists of
an elliptical plate positioned obliquely to the shaft.
As the plate and shaft rotate, the surface of the plate
moves to and fro lengthwise relative to the centerline
of the shaft. This reciprocating motion is transmitted
to the pistons which contact the surface of the wash
plate. A woodruff key locks the wash plate onto theshaft. The wash plate and shaft are serviced as an
assembly. The shaft is driven by a pulley when the
magnetic clutch is energized. A needle thrust bearing
and
L mainshaft bearing support the shaft horizon-
tally and vertically.
5. Needle Thrust Bearing and Races
- Two needle
thrust bearings, each“sandwiched” between two
races are located on either side of the wash plate
hub. The front needle thrust bearing and races pro-
vide 0.010” to 0.015” clearance between the top of
the pistons and the rear side of the front suction valve
reed disc (see Figure
9B-28). The rear needle thrust
bearings and races provide 0.0005” to 0.0015” clear-
ance between the hub of the wash plate and the rear
hub of the rear cylinder. Races of various thicknesses
are provided for service replacement to achieve re-
quired clearances when rebuilding units.
6. Cylinder Assembly and service Pistons (Factory
installed pistons are ringless) -The cylinder assembly
(front cylinder and rear cylinder) is serviced only as
a matched set. Alignment of the two halves is main-
tained by two dowel (locater) pins.
The double ended pistons are made of cast alumi-
num. There are two grooves on each end of the ser-
vice piston. The outer grooves will receive a piston
ring. The inner grooves act as oil scraper grooves to
collect any excess oil. Two oil return holes are drilled

REFRIGERANT COMPONENTS ALL MODELS9s. 35
THRUST UNITSHOES ARE USED
CONTROLS PISTONTO GIVE
HEAD CLEARANCE
.0005 TO .OOlOTOTAL\CLEARANCE
THRUST UNIT CONTROLSRUNNING CLEARANCE.0005 TO .0015
9B-25Figure 98-28 Compressor Needle Thrust Bearings and
into the scraper grooves and allow oil to drain back
into the reservoir.
7. Shoe Discs
- The shoe discs are made of bronze
and act as a bearing between the ball and the wash
plate. An oil circulation hole is provided through the
center of each shoe for lubrication purposes. These
shoes are of various thicknesses and are provided in
0.0005 inch increments. Ten sizes are available for
service replacement. A basic “zero” shoe size is
available’ for preliminary gauging procedures when
rebuilding a cylinder assembly.
8. Suction Passage Cover-The suction passage cover
fits over a suction passage (see Figure 9B-30) in the
body of the cylinder assembly. Low pressure vapor
SUCTION PASSAGECOVER
TUBE9B-26
Figure 98-30 Suction Passage and Discharge Tubeflows from the suction port through the suction pas-
sage in the cylinder assembly, and into the suction
cavity of the front head.
9. Discharge Tube
- The discharge tube is used to
connect the discharge cavity in the front head with
the discharge cavity in the rear head. High pressure
vapor discharge is channeled via the tube to the dis-
charge cavity and port. A slightly modified discharge
tube is provided to be used as a service replacement
(see Figure
9B-31). The service replacement tube has
a reduced end and a built up shoulder to accomodate
an “0” ring and bushing. These added parts achieve
the necessary sealing of the high pressure vapor
within the compressor.
DISCHARGE
TUBE
oeR’NG\s~~~~~~G98.27
Figure 98.31 Service Replacement Discharge Tube
10. Pressure Relief Valve
- The purpose of the pres-
sure relief valve is to prevent the discharge pressure
from exceeding 440 psi. Opening of the pressure re-
lief valve will be accompanied by a loud popping
noise and the ejection of some refrigerant from the
valve. If the pressure relief valve is actuated due to
excessive pressures in the compressor, the cause of
the malfunction should be corrected immediately.
The pressure relief valve is located on the rear head
of the compressor.
11. Shell and Oil Drain Screw
- The shell of the
compressor contains a reservoir which furnishes a
continuous supply of oil to the moving parts of the
compressor. A
batTIe plate covers the reservoir and