1973 OPEL MANTA oil pressure

REFRIGERANT COMPONENTS ALL MODELS99.29
1 REFRIGERANT LEAVES COMPRESSOR
AS A HIGH PRESSURE-HIGH
TEMPERATURE VAPOR
REFRIGERANT RETURNS TO
COMPRESSOR AS LOW PRESSURE VAPOR
EXPANSION VALVE5 HEAT REMOVED
FROM AIR VAPORIZES
LOW PRESSURE
LIQUID REFRIGERANT
4 HIGH PRESSURE‘JQUID CHANGES
TO LOW PRESSURE
LIQUID AT THIS
POINT
2 UPON REMOVAL OF HEAT
VAPOR BECOMES HIGH
PRESSURE LIQUID REFRIGERANT3 LIQUID REFRIGERANT IS STORED
HERE UNTIL NEEDED
98*II
Figure 98-23
Basic
Refrigeration Cyclewithin certain operating limits. If these limits are
exceeded, many physical and chemical reactions oc-
cur. Since the results of these reactions within the
system cannot be easily removed, they build up into
a constantly accelerating vicious circle to eventually
fail the system.is allowed to enter the system, it can start a chain of
chemical reactions which upsets stability and inter-
feres with the operation of the unit.
Metals
CHEMICAL INGREDIENTS OF AN AUTOMOTIVE
AIR CONDITIONING SYSTEMAll systems involve metals, refrigerant, and oil which
are basic and essential. The desiccant, or dehydrating
agent, and another chemical ingredient, synthetic
rubber, makes it even more complex.
All of these ingredients have chemical properties
which are entirely different from each of the others.
In spite,of these differences, by proper selection of
the ingredients and controlled processes in manufac-
ture, plus careful servicing procedures they can be
combined so that they “live together” to provide
many years of satisfactory and trouble-free operat-
ion.If, however, only one undesirable element is added orIn most cases, metals contribute to the decomposi-
tion of R-12 and oil in varying amounts. All are
attacked by acids.
Each of the metals in common use in a system has
been selected for a specific reason; heat conductivity,
durability, strength, and chemical composition.
Under favorable conditions, the amounts of decom-
position of Refrigerant-12 and oil produced by these
metals is negligible and allowable. However, if un-
desirable substances are added and the temperature
is increased, the rate of decomposition and the pro-
duction of harmful acids increases proportionally.
RefrigerantThe chemical properties of refrigerants are very im-
portant factors in the stability of a system since the

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.

REFRIGERANT COMPONENTS ALL MODELS99- 33
That the attraction of the drying material for mois-
ture is so powerful that if the receiver is left open,
moisture will be drawn in from the outside air.
That just one drop of water added to the refrigerantwill start chemical changes that can result in corro-
sion and eventual breakdown of the chemicals in the
system. Hydrochloric acid is the result of an R-12
mixture with water.
That the smallest amount of air in the refrigeration
system may start reactions that can cause malfunc-
tions.
That the drying agent in the receiver-dehydrator is
Activated Silica Alumina (silica-gel).
That
the inert gas in the expansion valve capillary
line is carbon dioxide.
DESCRIPTION OF AIR CONDITIONING
COMPONENTS
Compressor
The compressor is located in the engine compart-
ment. The purpose of the unit is to draw the low
pressure,gas from the evaporator and compress this
gas into a high temperature, high pressure gas. This
action will result in the refrigerant having a higher
temperature than the surrounding air.
The
cortipressor is of basic double action piston de-
sign. Three horizontal double acting pistons make up
a six cylinder compressor (See Figure
9B-162). The
pistons operate in
l-1/2 inch bore and have a l-1/8
inch stroke. A
wash plate keyed to the shaft drives
the pistons. The shaft is belt driven through a mag-
netic clutch and pulley arrangement. An oil pump
mounted at the rear of the compressor picks up oil
from the
botto’m of the compressor and lubricates the
bearings’and other internal parts of the compressor.
Reed type valves at each end of the compressor open
or close to control the flow of incoming and outgoing refrigerant. Two gas tight passages interconnect
chambers of the front and rear heads so that there is
one common suction port, and one common dis-
charge port. The internal parts of the compressor
function, as follows:
1. Suction Valve Reed Discs and Discharge Valve
Plates
_ The two suction valve reed discs and two
discharge valve plates (see Figure
9B-25) operate in
a similar but opposite manner. The discs are com-
posed of three reeds and function to open when the
pistons are on the intake portion of their stroke
(downstroke), and close on the compression stroke.
The reeds allow low pressure gas to enter the cylin- ders. The discharge valve plates also have three
reeds, however, they function to open when the pis- tons are on the compression portion of their stroke
(upstroke), and close on the intake stroke. High pres-
sure gas exits from discharge ports in the discharge
valve plate. Three retainers riveted directly above the
reeds on the valve plate serve to limit the opening of
the reeds on the compression stroke.
SUCTION VALVE
DISCHARGE-VALVE PLATES
Figure
98-25 - Compressor Suction Valve Reed Discs
and Discharge Valve Plates
2. Front and Rear Heads - The front and rear heads
(Figure
9B-26) serve to channel the refrigerant into
and out of the cylinders. The front head is divided
into two separate passages and the rear head is di-
vided into three separate passages. The outer passage
on both the front and rear heads channels high pres-
sure gas from the discharge valve reeds. The middle
passage of the rear head also contains the port open-
ing to the superheat switch cavity. This opening in
the rear head permits the superheat switch to be
affected by suction gas pressure and suction gas tem-
perature for the operating protection of the compres-
sor. The inner passage on the rear head houses the
oil pump inner and outer rotors. A Teflon sealing
material is bonded to the sealing surfaces separating
the passages in the rear head.
“0” rings are used to
affect a seal between the mating surfaces of the heads
and the shell. The front head suction and discharge
passages are connected to the suction and discharge
passages of the rear head by a discharge tube and
suction passage in the
body of the cylinder assembly.
A screen located in the suction port of the rear head
prevents foreign material from entering the circuit.
3. Oil Pump
- An internal tooth outer rotor and
external tooth inner rotor comprise the oil pump.
The pump works on the principle of a rotary type pump. Oil is drawn up from oil reservoir in underside
of shell through the oil inlet tube (see Figure
9B-27)

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

REFRIGERANT COMPONENTS ALL MODELS
99.37
in front of the radiator so that it receives a high
volume of air flow. Air passing over the condenser
absorbs the heat from the high pressure gas and
causes the refrigerant to condense into a high pres-
sure liquid.Receiver. DehydratorThe receiver-dehydrator is located in the engine
compartment. The purpose of the receiver dehydra-
tor is two fold: the unit insures a solid column of
liquid refrigerant to the expansion valve at all times,
and also absorbs any moisture in the system that
might be present. A bag of desiccant (moisture ab-
sorbing material) is provided to absorb moisture. A
sight glass (see Figure 9B-33) permits visual check-
ing of the refrigerant flow for bubbles or foam. The
continuous appearance of bubbles or foam above an
ambient temperature of 70 degrees F. usually indi-
cates an inadequate refrigerant charge. Bubbles or
foam appearing at ambient temperatures below 70
degrees F. do not necessarily indicate an inadequate
charge and may appear even when the system is
operating properly. A filter screen in the unit pre-
vents foreign material from entering the remainder
of the system.
Expansion ValveThe expansion valve is mounted on the evaporator
core inside the passenger compartment. The function
of the expansion valve is to automatically regulate
SCREEN
lLCl98.30
Figure 98-34 Expansion Valvethe flow of refrigerant into the evaporator. The ex-
pansion valve is the dividing point in the system
between the high and low pressure liquid refrigerant.
A temperature sensing bulb is connected by a capil-
lary tube to the expansion valve (see Figure
9B-34).The temperature sensing bulb (clamped to the outlet
pipe on the evaporator) measures the temperature of
the evaporator outlet pipe and transmits the temper-
ature variations to the expansion valve (see Figure
9B-34). The capillary tube and bulb are tilled with
carbon dioxide and sealed to one side of the expan-
sion valve diaphragm.
An increase in temperature will cause the carbon
dioxide in the bulb and capillary tube to expand,
overcoming the spring pressure and pushing the dia-
phragm against the operating pins (see Figure 9B-
34). This in turn will force the valve off its seat.
When the refrigerant low pressure gas flowing
through the outlet pipe of the evaporator becomes
more than 6 degrees higher or warmer than the tem-
perature at which it originally began to vaporize or
boil, the expansion valve will autmotatically allow
more refrigerant to enter evaporator. If the tempera-
ture of the low pressure gas decreases to less than 6
degrees above the temperature at which it originally
began to vaporize or boil, the expansion valve will
automatically reduce the flow of refrigerant. Thus,
an increase or decrease in the flow of refrigerant
through the evaporator will result in an increase or
decrease in the cooling by the evaporator. The tem-
perature, humidity and volume of the air passing
over the evaporator affects the rate of absorption of
heat by the evaporator. As the ambient temperature
bulb calls for more or less refrigerant will increase or
decrease. When the air is very warm, the heat trans-
fer from the air to the refrigerant is great and a
greater quantity of refrigerant is required to maintain
the temperature at the evaporator pipe at the prede-
termined value. Conversely, cool days will result in
less heat transfer and thereby require lesser quanti-
ties of refrigerant to maintain the predetermined
temperature of the evaporator outlet pipe.
EvaporatorThe function of the evaporator is to cool and
dehumidify the air flow in the passenger compart-
ment. The evaporator assembly consists of an alumi-
num core enclosed in a reinforced plastic housing.
Two (2) water drain ports are located in the bottom
of the housing. Two refrigerant lines are connected
to the side of the evaporator core: one at the bottom
and one at the top. The expansion valve is attached
to the lower (inlet) pipe, the outlet pipe is attached
to the upper pipe. The temperature sensing bulb of
the expansion valve is clamped to the outlet pipe of
the evaporator core. The high pressure liquid refrig-
erant, after it is metered through the expansion
valve, passes into the evaporator core where it is
allowed to expand under reduced pressure. As a re-
sult of the reduced pressure the refrigerant begins to

9B-38 1973 OPEL SERVICE MANUAL
expand and return to the original gaseous state. To
accomplish this transformation it begins to boil.
The boiling action of the refrigerant demands heat.
To satisfy the demand for heat, the air passing over
the core gives up heat to the evaporator and is subse-
quently cooled.\
DIAGNOSIS
GENERAL INFORMATIONThe following is a brief description of the type of
sympton each refrigerant component will evidence if
a malfunction occurs:
Compressor malfunction will appear in one of four
ways: noise, seizure, leakage, or low discharge pres-
sure.Resonant compressor noises are not cause for alarm;
however, irregular noise or rattles may indicate
broken parts or excessive clearances due to wear. To
check seizure, de-energize the magnetic clutch and
check to see if drive plate can be rotated. If rotation
is impossible, compressor is seized. Low discharge
pressure may be due to a faulty internal seal of the
compressor, or a restriction in the compressor.
Low discharge pressure may also be due to an insuffi-
cient refrigerant charge or a restriction elsewhere in
the system. These possibilities should be checked
prior to servicing the compressor. If the compressor
is inoperative; but, is not seized, check to see if cur-
rent is being supplied to the magnetic clutch coil
terminals.
CondenserA condenser may malfunction in two ways: it may
leak, or it may be restricted. A condenser restriction
will result in excessive compressor discharge pres-
sure. If a partial restriction is present, sometimes ice
or frost will form immediately after the restriction as
the refrigerant expands after pas?ing through the re-
striction. If air flow through the condenser or radia-
tor is blocked, high discharge pressures will result.
During normal condenser operation, the outlet pipe
will be slightly cooler than the inlet pipe.
Receiver-DehydratorA receiver-dehydrator may fail due to a restriction
inside body of unit. A restriction at the inlet to the
receiver-dehydrator will cause high head pressures.
Outlet tube restrictions will be indicated by low headpressures. Outlet tube restrictions will be indicated
by
low head pressures and little or no cooling. An
excessively cold receiver-dehydrator outlet may be
indicative of a restriction.
Expansion ValveExpansion valve failures usually will be indicated by
low suction and discharge pressures, and insuff%ient
evaporator cooling. The failure is generally due to
malfunction of the power element and subsequent
closing of the valve. A less common cause of the
above symptom is a clogged inlet screen.
EvaporatorWhen the evaporator malfunctions, the trouble will
show up as inadequate supply of cool air. A partially
plugged core due to dirt or a faulty blower will gener-
ally be the cause.
Refrigerant Line Restrictions
Rest~rictions in the refrigerant lines will be indicated
as follows:
I. Suction Line - A restricted suction line will cause
low suction pressure at the compressor, low dis-
charge pressure and little or no cooling.
2. Discharge Line -A restriction in the discharge line
generally will cause the pressure relief valve to open.
3. Liquid Line
- A liquid line restriction will be evi-
denced by low discharge and suction pressure, and
insufficient cooling.
Use of Receiver-Dehydrator Sight Glass for
DiagnosisAt temperatures higher than 70 degrees F, the sight
glass may indicate whether the refrigerant charge is
sufficient. A shortage of liquid refrigerant is in-
dicated after about
five minutes of compressor oper-
ation by the appearance of slow-moving bubbles
(vapor) or a broken column of refrigerant under the
glass. Continuous bubbles may appear in a properly
charged system on a cool day. This is a normal situa-
tion. If the sight, glass is generally clear and perform-
ance is satisfactory, occasional bubbles do not
indicate refrigerant shortage.
If the sight glass consistently shows foaming or a
broken liquid column, it should be observed after
partially blocking the air to the condenser. If under
this condition the sight glass clears and the perform-
ance is otherwise satisfactory, the charge shall be
considered adequate.