'November 1977'
MOTOR VEHICLE
EMISSIONS CONTROL
THERMOSTATIC AIR
CLEANER SYSTEMS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-77-037
MOTOR VEHICLE EMISSIONS CONTROL
BOOK TWO
THERMOSTATIC AIR
CLEANER SYSTEMS
by
B.D. Hayes, Project Director
M.T. Maness, Associate Project Director
R.A. Ragazzi, Principal Investigator
R.A. Barrett, Graduate Research Assistant
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
EPA Grants No. T008135-01-0 and T900621-01-0
EPA Region VIII Project Officer: Elmer M. Chenault
EPA Project Officer: Bruce Hogarth
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Control Programs Development Division
30 Research Triangle Park, North Carolina 27711
November 1977
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Copies of this publication are available free of charge to Federal employees,
current contractors and grantees, and nonprofit organizations - as supplies
permit - from the Library Services Office (MD-35), Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; or, for a fee, from
the National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22161.
This report was furnished to the Environmental Protection Agency by the
Department of Industrial Sciences, Colorado State University, Fort Collins,
Colorado, 80523, through Grants No. T008135-01-0 and No. T900621-01-0.
The contents of this report are reproduced herein as received from Colorado
State University. The opinions, findings, and conclusions expressed are
those of the authors and not necessarily those of the Environmental Protection
Agency. Mention of company or product names is not to be considered as
an endorsement by the Environmental Protection Agency.
Publication No. EPA-450/3-77-037
ii
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ACKNOWLEDGMENTS
The Motor Vehicle Emissions Control Staff of the Department
of Industrial Sciences at Colorado State University would
like to acknowledge the efforts extended by the Environmental
Protection Agency, Research Triangle Park, and Region VIII
Environmental Protection Agency, Manpower Development
Division.
A special thanks must be extended to the automotive vehicle
equipment and parts manufacturers for their cooperation and
assistance in the development of this training material.
iii
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MOTOR VEHICLE EMISSIONS CONTROL
-- SERIES OF SEVEN BOOKS --
MOTOR VEHICLE EMISSIONS STAFF, COLORADO STATE UNIVERSITY
BOOK ONE - POSITIVE CRANKCASE VENTILATION SYSTEMS
BOOK TWO - THERMOSTATIC AIR CLEANER SYSTEMS
BOOK THREE - AIR INJECTION REACTION SYSTEMS
BOOK FOUR - FUEL EVAPORATION CONTROL SYSTEMS
BOOK FIVE - EXHAUST GAS RECIRCULATION SYSTEMS
BOOK SIX - SPARK CONTROL SYSTEMS
BOOK SEVEN - CATALYTIC CONVERTER SYSTEMS
IV
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INSTRUCTIONS FOR THE USE OF THIS BOOK
This book is one of a series designed specifically to teach the concepts
of automobile emissions control systems. Each book is designed to be
used as self-instructional material. Therefore, 1t is important that
you follow the step-by-step procedure format so that you may realize the
full value of the emissions system which 1s being presented. The topics
are taught in incremental steps and each topic treatment prepares the
student for the next topic. Each book 1s divided into sections which
Include the introduction, purpose, function, inspection and testing of
the emissions system presented.
As you proceed through this series, please begin with book one and read
the following books in sequence. This 1s important because there are
several instances where material covered in a given book relies on
previously covered material in another book.
To receive the full benefits of the book, please answer the self-
evaluation statements related to the material. These statements are
separated from the text by solid lines crossing the page. The answers
to the statement can be found at the end of the book as Identified by
the table of contents. You should check for the correct answer after
you respond to each statement. If you find that you have made a mistake,
go back through the material which relates to the statement or statements.
Fi1l-1n-the-blank statements are utilized for self-evaluation purposes
throughout the material. An example statement would appear like this:
The American flag is red, white, and
You would write "blue" In the blank and immediately check your answer at
the end of the book.
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The material, statements and illustrations should be easy to follow and
understand. In several illustrations a small ghost named "VEC" (Vehicle
Emissions Control) has been used to make the picture easier to understand.
Upon completion of this series, you should be able to better understand
the emissions control systems and devices which are an integral part of
automobiles today. Your increased knowledge should help you keep these
"emissions controlled" vehicles operating as they were designed to
operate. Respectable fuel economy, performance and driveability, as well
as cleaner air, can be obtained from the automobile engine that has all
of its emissions systems functioning properly.
vi
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CONTENTS
Introduction to Emissions Control 2-1
Hydrocarbons 2-1
Carbon Monoxide 2-1
Oxides of Nitrogen 2-2
Formation of Hydrocarbons 2-2
Formation of Carbon Monoxide 2-3
Formation of Oxides of Nitrogen 2-3
Ignition Timing 2-3
Carburetion 2-5
System Introduction 2-7
System/Component Purpose 2-11
Thermostatic Type Air Cleaner 2-11
Vacuum Override Motor 2-13
Air Valve Type Air Cleaner 2-15
Air Bleed Valve-Temperature Sensor 2-17
System/Component Function 2-19
Thermostatic Type Air Cleaner 2-19
Vacuum Override Motor 2-22
Air Valve Type Air Cleaner 2-25
System Inspection 2-33
System Testing 2-35
Thermostatic Type Air Cleaner Test 2-35
Vacuum Override Motor Test 2-37
Air Valve Type Air Cleaner Test 2-38
Summary 2-45
Answers 2-47
vii
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INTRODUCTION TO EMISSIONS CONTROL
As we all know emissions systems and devices have been installed on the
automobile engine because of the air pollution problem. In order for
you to understand these emissions systems and devices you should have a
background of the problem. All of the emissions control systems were
installed on the engine to reduce just three specific exhaust products.
These are known as products of combustion. The three products which the
emissions systems are designed to reduce are hydrocarbons, carbon monoxide
and oxides of nitrogen.
HYDROCARBONS
Gasoline, like all petroleum products, is made up of hundreds of hydro-
carbon compounds. The name "hydrocarbon" has been given to these com-
pounds because they are made up of hydrogen and carbon atoms. This is
also the reason hydrocarbons have the abbreviation (HC).
Hydrocarbons are gasoline vapors or raw gasoline itself. One reason
hydrocarbon emissions must be controlled is because it is one of the
major components of photochemical smog. Photochemical or "Los Angeles"
smog forms when hydrocarbons and oxides of nitrogen combine in the
presence of sunlight. In order to avoid this smog condition the hydro-
carbon emissions from automobiles must be controlled. Hydrocarbons
also act as an irritant to our eyes and some are suspected of causing
cancer and other health problems.
CARBON MONOXIDE
Another product of combustion that must be controlled is carbon monoxide.
Carbon monoxide has the abbreviation (CO). CO is also hazardous to our
health when it is mixed with the air we breathe. It can cause headaches,
reduce mental alertness and even cause death if enough of it is in the
air. Carbon monoxide is also a problem in that it speeds the formation
of photochemical smog. For these reasons CO emissions must be controlled.
2-1
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2-2
OXIDES OF NITROGEN
Oxides of nitrogen are the last harmful products of combustion we will
discuss. Nitrogen oxides have been given the abbreviation (NO ). As
/\
you already know, oxides of nitrogen and hydrocarbons combine to form
photochemical smog. The sunlight which triggers the formation of photo-
chemical smog has another effect on oxides of nitrogen. Some of the
oxides of nitrogen are broken down and a gas called ozone is formed.
Ozone is a lung and eye irritant and it also deteriorates rubber and
affects the growth of vegetation. Since the nitrogen oxides have these
effects they must also be controlled.
Now that you are familiar with the emissions which must be controlled
let's find out where they originate.
FORMATION OF HYDROCARBONS
Hydrocarbons, you will recall, are fuel vapors or raw fuel. For this
reason hydrocarbon emissions will result from any uncontained supply
of gasoline. Hydrocarbon emissions also come from the tailpipe. If
the automobile engine could achieve "complete combustion," all of the
unburned fuel or hydrocarbons would be used up. However, it is impos-
sible for today's automobile engines to achieve "complete combustion."
Any time the fuel mixture in the combustion chamber is not completely
burned, some hydrocarbons will be emitted from the tailpipe. The two
main reasons why hydrocarbons are not completely burned are because of
engine misfire and "quench areas." When an engine misfire occurs, none
of the raw fuel or hydrocarbons are burned. When this happens they are
simply exhausted directly to the atmosphere. Quench areas are places in
the combusion chamber where the flame goes out before the fuel is com-
pletely burned. Small cavities such as where the head gasket seals the
cylinder head to the block is a quench area. Another quench area is
located between the top of the piston and the first compression ring.
These areas are sources of hydrocarbon emissions.
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2-3
FORMATION OF CARBON MONOXIDE
Carbon monoxide is partially burned fuel. Carbon monoxide is formed in
the combustion chamber whenever there is not enough air to burn all the
fuel. This means that whenever a "rich" air/fuel mixture is pulled into
the combustion chamber carbon monoxide will be formed. After the flame
goes out the carbon monoxide is exhausted through the tailpipe and into
the air.
FORMATION OF OXIDES OF NITROGEN
Oxides of nitrogen are also formed in the combustion chamber. These
oxides result from the nitrogen which is contained in our air. In some
cases combustion temperatures in the automobile engine can exceed 4500°F.
At temperatures above approximately 2500°F, nitrogen oxides will start
forming. Therefore, If combustion chamber temperatures exceed 2500°F,
oxides of nitrogen will be produced and then exhausted to our atmosphere.
Now that you understand how these emissions are formed in the automobile
engine, we will see how changes in ignition timing and carburetor adjust-
ment affect the amount of these pollutants.
As you know, changes in timing and carburetion can have a large effect on
how an engine performs. These changes in timing and carburetion also can
have drastic effects on the amount of pollutants which are present in the
automobile's exhaust. The amount of hydrocarbons, carbon monoxide and
oxides of nitrogen which are present in the exhaust gases will vary as
timing and carburetion adjustments are changed.
IGNITION TIMING
Prior to emissions controlled automobiles, advancing the spark timing
was a common practice. Setting the spark timing this way caused the
spark plug to fire before the piston reached top dead center. This
advanced spark timing allowed the maximum amount of heat energy to be
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2-4
exerted on the piston. As a result the best performance and fuel econ-
omy could be obtained. Unfortunately, this also produced high hydro-
carbon and nitrogen oxide emissions .levels.
In order to reduce emissions levels, ignition spark timing was retarded.
By firing the spark plug after the piston reaches top dead center, not
as much of the heat energy is converted to work on the piston. The
extra heat energy which is not used on the piston now passes through
the exhaust valve and into the exhaust manifold. This keeps the exhaust
gas temperatures higher. These higher exhaust temperatures allow burning
of the air/fuel mixture to continue in the exhaust manifold. This further
oxidation or burning in the exhaust manifold helps to reduce HC and CO
emissions.
Another advantage of retarded timing from an emissions standpoint is
that combustion temperatures are not as high. This is due to the fact
that the maximum combustion pressure will be lower. Since the combustion
temperatures will be lower and the formation of oxides of nitrogen de-
pends on temperature, a smaller amount of these pollutants will be ex-
hausted to the atmosphere.
There is one more advantage to using retarded spark timing. As you know,
when ignition timing is retarded the engine's idle speed will drop. This
decrease in idle speed occurs because less heat energy is applied to the
combustion chamber and more heat energy is being supplied to continue the
burning process in the exhaust manifold. In order to regain an acceptable
idle speed, the throttle plates must be opened wider. This wider throttle
plate opening allows more air to pass through the carburetor. This increase
in air flow will reduce the amount of residual exhaust gases in the cylinder.
This in turn will allow a more burnable mixture which can be made leaner.
Since the mixture can be leaner there will be more air in the combustion
chamber. As you know, the more air that is made available during com-
bustion the lower will be the HC and CO emissions.
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2-5
CARBURETION
Adjustments made to the carburetor air/fuel ratio can also have a large
effect on the amount of pollutants which come from the automobile engine.
When idle mixture settings become richer there is less air present for
the combustion process. This lack of air results in an increase in hydro-
carbon and carbon monoxide emissions.
When the idle mixture screws are turned in, the amount of fuel is reduced
and the mixture becomes leaner. This leaner mixture contains more air
and therefore more oxygen is available for more complete burning of the
fuel. This results in lower HC and CO emissions levels.
As the idle mixture screws are turned in, the idle air/fuel mixture be-
comes leaner. If this mixture becomes too lean a "lean misfire" will
occur. A "lean misfire" will occur because the fuel is so diluted or
thinned out by the air that the mixture will not ignite. This leads to
a very large increase in hydrocarbon emissions. This happens because
the failure of the mixture to ignite results in that amount of raw fuel
being emitted to the atmosphere.
The carbon monoxide emissions decrease when a lean misfire condition is
present. Carbon monoxide is partially burned fuel. Since no combustion
takes place during a lean misfire condition no CO is formed and the total
amount of CO produced by the engine will be less.
A lean misfire usually occurs in one or more cylinders. This condition
may also move from cylinder to cylinder while the engine is running.
This is caused by the uneven distribution of the air/fuel mixture
delivered to each cylinder. This condition occurs mainly because of
problems with intake manifold design.
Now you should understand how changes in timing and^carburetion adjust-
ment can affect emissions levels. With thisj^knowtedge you will be able
to understand how each emissions;control system we will discuss helps to
reduce the air pollution caused by the automobile.
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TAG
2-7
SYSTEM INTRODUCTION
The next emissions control system we will examine is the Thermostatic Air
Cleaner system, abbreviated TAG. The TAG system helps in controlling auto
emissions and also increases vehicle performance and driveability.
Certain engineering changes on late model engines were necessary to obtain
the most "complete combustion" with the least amount of air pollution.
The TAG system is one of these engineering changes. By varying the
necessities of combustion (air, fuel, spark timing, etc.) we may obtain
a higher combustion efficiency and lower emissions. As you know, two of
the most common emissions are hydrocarbons (HC) and carbon monoxide (CO).
These pollutants are produced because of "incomplete combustion."
Incomplete combustion occurs when all of the air/fuel mixture entering the
engine is not used in the combustion process. When the combustion process
is not complete, some of the unused air/fuel mixture is exhausted to the
atmosphere. These left-over products of combustion are hydrocarbon and
carbon monoxide emissions. One method used to help limit the amount of
HC and CO in the automobile's exhaust is to provide a leaner air/fuel
mixture to the engine. This means less fuel is mixed with the air enter-
ing the carburetor. This increases the efficiency of the combustion
process and leaves fewer left-over HC and CO pollutants to go into the
exhaust. There is a problem, however. This leaner air/fuel mixture
burns well when the engine has been warmed up and is running at a relatively
high temperature. The problem occurs when using a lean mixture in a cold
engine.
Before the engine is warmed up to normal operating temperature we usually
"choke" the carburetor. This provides a very "rich" air/fuel mixture to
the engine. A mixture rich in fuel is necessary to obtain satisfactory
performance with a cold engine. When gasoline leaves the carburetor it
must atomize to be easily mixed with the air. Atomization is the process
of breaking down the fuel into small particles to form a vapor to mix with
the air entering the carburetor. The air and fuel must be thoroughly
mixed for a more complete combustion to occur.
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2-8
This is easily accomplished when the engine has been warmed up. When the
engine is warm, the air entering the carburetor is at a temperature high
enough to rapidly atomize the fuel. When the engine is cold however, the
carburetor is cold and the air entering the carburetor is also cold. This
causes problems in the fuel atomization process. The atomization of fuel
can be compared to the evaporation or vaporization of water on a hot day
in summer compared to a cold day in winter. When the air temperature is
high, atomization occurs much easier. Fuel atomizes much easier with warm
A
air than with cold air. When the fuel is not atomized completely the
engine operates rough because the air/fuel mixture will not burn smoothly.
Under certain cold conditions, when the air entering the carburetor is
insufficient to warm the fuel, a freezing of the air/fuel mixture may
occur. This is called "carburetor icing."
What is now used to eliminate this cold engine problem is the Thermostatic
Air Cleaner (TAG). The TAG system was first introduced on some 1966
automobiles. This thermostatic (heat-activated) air cleaner provides
heated air to the carburetor during warm-up operations. Air is heated
by the exhaust manifold before entering the carburetor.
EXHAUST MANIFOLD
PIPE
(HOT AIR
PIPE)
FILTER
EXHAUST MANIFOLD
EXHAUST MANIFOLD
HEAT SHROUD
FIGURE. 2-1
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TAG
2-9
Heated air entering the carburetor allows better fuel atomization,
smoother cold engine performance and helps reduce carburetor icing. The
thermostatic air cleaner provides heated air only during the engine warm-
up period. The air temperature is regulated as needed during this time.
After the engine has been warmed-up and no longer needs heated air,
normal engine compartment air is provided as with conventional air
cleaner systems. The thermostatic air cleaner permits smooth engine
operation while using a lean air/fuel mixture at all times.
During warm-up periods heated air is provided. During normal operating
conditions engine compartment air is supplied. The TAG system eliminates
much of the hydrocarbon and carbon monoxide emissions usually formed
during cold engine warm-up.
1. TAG means
2. The TAG system helps control auto emissions. It also
increases vehicle performance and
3. Two of the most common emissions are hydrocarbons and
carbon monoxides. These pollutants are produced because
of
4. One method used to help limit the amount of HC and CO in
auto emissions is to provide a air/fuel mixture
to the engine.
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2-10
5. is the process of breaking down
the fuel into small particles to form a vapor to unite
with the air entering the carburetor.
6. Fuel atomizes much easier with air than with
cold air.
7. The thermostatic air cleaner provides
to the carburetor during engine warm-up operations,
8. The TAG system provides heated air only during the engine
- periods.
9. The TAG system eliminates much of the HC and
emissions usually formed during cold engine warm-up.
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TAG
2-11
SYSTEM/COMPONENT PURPOSE
The introduction explained how heated air, provided during warm-up
operation would benefit engine performance. The purpose of the Thermo-
static Air Cleaner is to provide heated air. The TAG system provides
this heated air and regulates the temperature at which it enters the
carburetor. Therefore, the TAG system improves cold engine performance
and reduces emissions by warming the air used for the combustion process,
There are two widely used types of thermally activated systems. One is
called a thermostatic type, the other an air valve type. You will see
that although the component parts of the two differ somewhat, the
purpose of both is to control intake air temperature.
THERMOSTATIC TYPE AIR CLEANER
The" main component acting on intake air entering the carburetor is the
air cleaner. The air cleaner is composed of two main parts: the main
body, containing the filter and air inlet tube or snorkel. With both
types of TAG systems we have an opening in the bottom of the snorkel to
which is attached an exhaust manifold pipe or hot air pipe. This pipe
connects the opening in the snorkel to an exhaust manifold heat shroud.
EXHAUST MANIFOLD
PIPE SNORKEL
(HOT AIR 7i0iqiELr
PIPE)
FILTER
EXHAUST MANIFOLD
EXHAUST MANIFOLD
HEAT SHROUD
FIGURE 2-2
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2-12
These two components form a heat path to the air intake system. Heat is
picked up by air passing through the shroud. The heated air is drawn up
through the hot air pipe to the snorkel.
10. There are two widely used types of thermostatic air
cleaner systems. One is called a
type. The other is called an air valve type.
11. Both types of TAG systems have an opening in the bottom
of the snorkel to which is attached a
pipe.
AIR VALVE DOOR
The next component we will look at is the air valve or air valve door.
The air valve door is located inside the snorkel and above the hot air
AIR VALVE (DOOR)
FILTER
TO EXHAUST
MANIFOLD SHROUD
FIGURE 2-3
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TAC
2-13
pipe. The valve is hinged on one side acting as a door to the hot air
coming from the exhaust manifold heat shroud. The air valve door is
connected to an air door spring. This spring holds the air door up,
blocking cold engine compartment air from entering the snorkel. This
allows hot air to enter from the hot air pipe.
To regulate the temperature of air entering the carburetor the TAC
system mixes relatively cold engine compartment air with heated air.
The door should be open to the hot air pipe allowing heated air to enter
during engine warm-up periods. During warm-up it should prevent cold
engine compartment air from entering. When the engine has been warmed up
and is operating at normal temperature, the door should cover the hot air
pipe and allow only cooler engine compartment air to enter.
THERMOSTAT
The door operation is controlled by a thermostat connected to the air door
near its hinge or pivot point. The thermostat is a heat sensing device that
operates the air valve door as determined by the temperature of the intake
air.
VACUUM OVERRIDE MOTOR
Figure 2-3 shows the basic components used in thermostat!c type air
cleaners. One additional device however is sometimes used on this type
system. A Vacuum Override Motor seen in figure 2-4 may be attached to
TAC WITH VACUUM OVERRIDE MOTOR
AIR DOOR SPRING
iUUM OVERRIDE
MOTOR
TO INTAKE
MAMIFOLD VACUUM
FIGURE 2-4
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2-14
the snorkel and connected to the thermostat and air door by an override
lever. The motor uses intake manifold vacuum. The override motor is
used only during cold engine acceleration. We have seen that when the
engine is cold the air valve door is closed to engine compartment air
and is passing air from the hot air pipe. During cold engine acceleration
however, more air is needed by the engine than can be supplied through
the hot air pipe. The purpose of the vacuum override motor is to over-
ride the thermostatic control of the air valve door. This provides air
from both the engine compartment and the hot air pipe in a sufficient
amount to sustain cold engine acceleration.
12. Located inside the snorkel and above the hot air pipe
opening is an door.
13. To control the temperature of air entering the carburetor,
the TAG system mixes heated air and _^_^
air before it enters the air
cleaner.
14. Sometimes a ' . motor is
attached to the snorkel and air door on the thermostatic
type system.
15. The vacuum override motor is operated by
vacuum.
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TAG
2-15
16. The vacuum override motor's purpose is to override the
control of the air valve door during cold engine
AIR VALVE TYPE AIR CLEANER
Next we will look at the Air Valve Type air cleaner. As mentioned before,
the purpose of both the Thermostat!c Type and Air Valve Type air cleaner
is the same -- to heat air entering the carburetor and insure a warm air/
fuel mixture during cold engine operation. By heating the air we
eliminate many of the HC and CO emissions which occur during engine warm-
up and cold engine operation.
When describing components of the Air Valve Type air cleaner you will see
many are similar to the Thermostatic Type. The differences occur in the
method of regulation.
As with the Thermostatic Type system, we have an air cleaner consisting
of a filter and a snorkel as seen in figure 2-5. The snorkel has an
EXHAUST MANIFOLD
PIPE
(HOT AIR
PIPE)
SNORKEL
FILTER
EXHAUST MANIFOLD
HEAT SHROUD
FIGURE 2-5
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2-16
opening through which heated air enters. The heat collector is again
the exhaust manifold heat shroud, connected to the snorkel opening by a
hot air pipe.
AIR VALVE DOOR
As with the Thermostatic Type system, the heat path opening is regulated
by an air valve door. It is the air door that regulates the amount of
cold engine compartment air and warm, exhaust-heated air entering the
system. In the Air Valve Type system, the air door is operated by a
vacuum motor. As seen in figure 2-6, a vacuum hose runs from the intake
manifold to a vacuum motor positioned on top of the snorkel. The vacuum
motor has a linkage connecting it to the air door.
AIR VALVE TYPE AIR CLEANER
VACUUM MOTOR
VACUUM HOSE
J
oo
oo
00
TO EXHAUST
MANIFOLD
. SHROUD
TEMPERATURE
SENSOR
(AIR BLEED
VALVEK
FIGURE 2-6
As vacuum reaches the vacuum motor the air door is lifted up limiting
engine compartment air and allowing heated air to enter the system. The
amount of intake manifold vacuum reaching the vacuum motor determines the
position of the air door. This vacuum is carried by a vacuum hose routed
through the air cleaner body. Located on the vacuum hose in the air
cleaner body is an air bleed valve.
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TAG
2-17
AIR BLEED VALVE-TEMPERATURE SENSOR
The air bleed valve controls the amount of vacuum in the vacuum hose.
When the air bleed valve opens, the vacuum in the hose is released.
When and how much the air bleed valve opens is determined by a temperature
sensor on the air bleed valve. This means both the amount of vacuum
reaching the vacuum motor and the temperature of air entering the system
is controlled by a temperature sensing device.
Now that you are familiar with the purpose of the components in the TAG
system it is time to learn how they function.
17. With the air valve type TAG system the amount of intake
manifold vacuum received by the vacuum motor determines
the position of the
18. An is located in the vacuum
hose in the air cleaner body.
19. When and how much the air bleed valve opens is determined
by the • .
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TAC
2-19
SYSTEM/COMPONENT FUNCTION
The purpose of the TAC system 1s to provide heated air to the carburetor.
The function of the system is to control the temperature of the intake
air. This is done by regulating the position of the air valve door. By
changing the position of this door the TAC system controls the amount of
heated air entering the system and thereby controls the temperature of
air entering the carburetor.
THERMOSTATIC TYPE AIR CLEANER
We will now examine how the Thermostatic Type system functions. As you
recall, the air door is connected to a spring and a thermostat. In the
cold start position the spring holds the air door up. This allows only
heated air to enter the system. Remember, the heated air has been warmed
by passing through the exhaust manifold heat shroud. This air door
position 1s called the "Hot A1r Mode."
20. The TAC system functions to the tempera-
ture of the air entering the carburetor.
HOT AIR MODE
When the TAC system 1s in the hot air mode, air from the engine compart-
ment is blocked from entering the system. Only heated air will be
allowed to enter the carburetor. The door is in the "Hot Air Mode" when
air entering the system is below approximately 100°F. The system would
be in this position when a cold engine has just been started. It would
also be in this position if the engine was off and cold.
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2-20
HOT AIR MODE
INCOMING AIR TEMPERATURE
BELOW APPROX. IOO°F
HOT AIR
FIGURE 2-7
REGULATING MODE
As the temperature of the air entering from the hot air pipe reaches
approximately 100°F the thermostat becomes activated. Remember a thermo-
stat is just a temperature sensing device. The thermostat is connected
to the air door by a rod. As the temperature rises above 100°F, the
REGULATING MODE
INCOMING AIR TEMPERATURE
BETWEEN APPROX. KX>-I3O°F
FIGURE 2-8
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TAG
2-21
thermostat begins to extend; this pushes the rod and moves the door away
from the "Hot Air Mode" into the "Regulating Mode." In this mode both
heated air and cooler engine compartment air enter the system. The amount
of heated and cool air is regulated by the thermostat which controls the
position of the door. The system is in the "Regulating Mode" when the
temperature is between approximately 100°F and 130°F. This temperature
range will occur after the engine has been started and is approaching
operating temperature.
COLD AIR MODE
When the temperature of the air passing the thermostat on its way to the
carburetor has reached approximately 130°F the air door will be completely
closed to heated air. This position is called the "Cold Air Mode."
COLD AIR MODE
INCOMING AIR TEMPERATURE
ABOVE APPROX. I30*F
FIGURE 2-9
The system will be in this position when the engine has warmed up. All
air entering the carburetor will now be coming from the engine compartment.
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2-22
21. The air door will be in the
when air entering the system is below approximately
100°F.
22. As the temperature rises above 100°F, the air door will
move away from the "Hot Air Mode" into the
23. When the temperature of the air has reached approximately
130°F, the door will be completely closed to heated air.
This position is called the " . "
24. In the Regulating Mode both heated air from the heat
shroud and cooler
air enters the system.
25. In the " " only cooler engine
compartment air can enter the system.
VACUUM OVERRIDE MOTOR
We have discussed the way all thermostat!c type air cleaners work. How-
ever, some systems include an additional vacuum override motor. You will
recall that the vacuum override motor was used to provide additional air
during cold acceleration. During engine warm-up when the air door is
in the "hot air mode" or beginning stages of the "regulating mode," only
-------
TAG
2-23
a limited supply of air is entering the system. This is obvious since the
air door is blocking much of the engine compartment air from entering the
system. Also the engine compartment is the main source of air for the
carburetor. During cold acceleration more air is needed to sustain the
engine than can be supplied from the hot air pipe. Therefore, we use a
vacuum override motor to override the thermostatic control of the air door
and allow more engine compartment air to enter. Figure 2-10 shows a cut-
away view of the vacuum override motor. The override motor is connected
TAG WITH VACUUM OVERRIDE MOTOR
AIR OOOR SPRING
THERMOSTAT
VACUUM OVERRIDE
MOTOR
TO INTAKE
MANIFOLD VACUUM
FIGURE 2-10
to the air door on one end and to an intake manifold vacuum hose on the
other. The motor is made up of a spring and a diaphragm. As you can see
in Figure 2-11, when the engine is at idle, there is high intake manifold
vacuum. This vaucum will pull the motor diaphragm back and allow the air
door to be pulled up by the air door spring. As the temperature increases
the thermostat will begin to close the door as usual. However, if accel-
eration is needed before the thermostat has opened the system to engine
compartment air, there would not be enough air to supply the engine. With the
vacuum override motor, when the throttle is opened, the intake manifold
loses much of its vacuum. This allows the spring in the motor to push
the diaphragm and rod forward. Pushing the rod forward overcomes spring
-------
2-24
AIR DOOR IN HOT AIR MODE AT IDLE
TO INTAKE
MANIFOLD
VACUUM
HEAT DOOR IN PARTIAL HEAT-OFF
POSITION UNDER COLD ACCELERATION
LOW OR NO
VACUUM
FIGURE 2-11
tension on the door and allows engine compartment air to enter. This will
happen regardless of the position of the thermostat.
The action of the vacuum override motor essentially forces the system into
a "regulating mode" regardless of the temperature of the entering air.
One more thing to remember about a thermostatic system with a vacuum over-
ride motor is that when the engine is off the hot air door will be down,
-------
TAG
2-25
in a "cold air mode." In systems without the vacuum override motor the
air door would be in the "hot air mode" because of the spring connected
to the door. In a system with the vacuum override motor, the spring
connected to the door would also try to hold the door up, but with the
engine off there would be no intake manifold vacuum. With no vacuum,
the motor's spring would force the door down just as in cold acceleration.
26. The override motor is connected by a linkage to the air
door on one end. It also has an
vacuum hose connection on the other end,
27. The vacuum override motor essentially forces the system
into a " " regardless of the
temperature of the entering air.
AIR VALVE TYPE AIR CLEANER
The purpose of the Air Valve Type air cleaner as mentioned before is to
provide heated air to the carburetor during warm-up operations. The
Air Valve Type system functions somewhat differently than the Thermostatic
Type, but the purpose is the same.
This system regulates the position of the air door according to
intake manifold vacuum. The air door is linked mechanically to a vacuum
motor mounted on top of the snorkel above the hot air pipe. The motor
consists of a spring and a diaphragm assembly much like a vacuum override
motor. A vacuum hose connects the vacuum motor to the intake manifold.
This hose runs through the air cleaner. Located on the hose inside the
air cleaner is a temperature sensor. This temperature sensor is the
device that controls the vacuum signal. Vacuum for the motor is supplied
by the intake manifold. The temperature sensor controls the vacuum
-------
2-26
AIR VALVE TYPE AIR CLEANER
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
oo
00
00
00
oo
00
oo
AIR VALVE
(DOOR)
TO EXHAUST
MANIFOLD —
L SHROUD
TEMPERATURE
SENSOR
(AIR BLEED
VALVE)
TO
MANIFOLD
FIGURE 2-12
signal to the vacuum motor by using an air bleed valve and a temperature
sensing spring or thermostat.
AIR BLEED
VALVE
CLOSED
TEMPERATURE
SENSING
SPRING
FULL
VACUUM
SIGNAL TO
VACUUM MOTOR
TO MANIFOLD
VACUUM
FIGURE 2-13
-------
TAC
2-27
HOT AIR MODE
When a cold engine is started and the temperature of the air passing the
temperature sensing spring is below approximately 85°F, full vacuum is
allowed to the vacuum motor. Full vacuum is allowed below approximately
85°F and the temperature sensing spring keeps the air bleed valve closed.
As you can see in figure 2-13, this allows a full vacuum signal to reach
the vacuum motor. When the temperature sensor allows a full vacuum signal
to reach the vacuum motor, such as when the temperature is below approxi-
mately 85°F, the system is in the "Hot Air Delivery Mode." This is shown
in figure 2-14.
HOT AIR DELIVERY MODE
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
J
oo
00
oo
Trfcjnro »•
oo
SENSOR
FIGURE 2-14
In the "Hot Air Delivery Mode" the vacuum draws the motor diaphragm up,
overcoming the diaphragm spring tension. Because the air door is linked
to the diaphragm spring, as the spring is pulled up by vacuum the air door
is also pulled up'. This opens the system to heated air from the hot air
pipe. In the Hot Air Delivery Mode cooler engine compartment air is
prevented from entering the system.
-------
2-28
REGULATING MODE
When the temperature of the air passing the temperature sensing spring in
the air cleaner rises above approximately 85°F the air bleed valve begins
to open. The sensor has reacted to the increase in temperature. As it
AIR BLEED
PARTIALLY
OPEN
TEMPERATURE
SENSOR
SPRING
TO V
VACUUM^
MOTOR
WEAKENED
VACUUM SIGNAL
TO MANIFOLD
VACUUM
FIGURE 2-15
senses these warmer temperatures it forces the air bleed valve to allow
atmospheric pressure to bleed into the vacuum line. This reduces the
vacuum signal to the vacuum motor. The weakened vacuum signal can no
longer hold the diaphragm spring and the spring tension starts to close
the air door. It has now moved to the "Regulating Mode."
In the Regulating Mode both heated air from the exhaust manifold and
cooler engine compartment air enter the system. The air door begins to
move down at a temperature of approximately 85°F. It is fully closed
when the temperature of air passing the temperature sensing spring is
approximately 130°F.
-------
TAG
2-29
REGULATING MODE
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
-AIR FILTER
TEMPERATURE
SENSOR
FIGURE 2-16
COLD AIR MODE
When the temperature of air passing the temperature sensing spring reaches
approximately 130°F or above, the air bleed valve has opened completely.
The air bleed valve now allows atmospheric pressure into the hose at such
a rate that it eliminates the vacuum reaching the vacuum motor.
AIR BLEED
OPEN
TEMPERATURE
SENSOR
SPRING
LOW
OR NO
VACUUM
SIGNAL
TO
VACUUM
MOTOR
TO MANIFOLD
VACUUM
FIGURE 2-17
-------
2-30
The vacuum signal can no longer overcome the diaphragm spring tension on
the vacuum motor. The air door is forced closed to heated air. The
system is now in the "Cold Air Mode."
COLD AIR DELIVERY MODE
DIAPHRAGM SPRING
VACUUM MOTOR
DIAPHRAGM \
oo
oo
oo
00
00
^^^AIR F
FILTER
TEMPERATURE
SENSOR
BLEEDING '
AIR
FIGURE 2-18
In the Cold Air Mode only cooler engine compartment air can enter the
system. This operating mode is used whenever the vacuum can no longer
overcome the diaphragm spring tension. This occurs when either the
temperature sensing spring has opened the air bleed valve to atmospheric
pressure (temperature above approximately 130°F) or when intake manifold
vacuum is too low to overcome the spring tension.
28. When the intake air passing the temperature sensor in
the air cleaner rises above approximately 85°F, the air
bleed valve begins to .
-------
TAG
2-31
29. When the engine has reached normal operating temperature
the air bleed valve will be fully .
30,
The air door is held in the hot air mode by
COLD ACCELERATION
You will recall that under certain cold acceleration conditions more air
is needed by the engine than can be supplied through the hot air pipe.
In the Thermostatic Type air cleaner a vacuum override motor was used to
supply more air. The Air Valve Type air cleaner does not need such a
device. During acceleration the carburetor throttle plates open. This
reduces manifold vacuum. With low manifold vacuum, the vacuum signal to
the vacuum motor is too weak to overcome the spring tension holding the
door closed to engine compartment air. Thus the volume of air required
for acceleration is provided regardless of the air temperature passing
the sensor.
LOW VACUUM CONDITION
VACUUM MOTOR
DIAPHRAGM SPRING
FILTER
/
00
oo
00
^^^..^-•AIK r
TEMPERATURE
SENSOR
\
FTGIIRF ?-!Q
-------
2-32
With the engine off or during low vacuum conditions the air door blocks
the hot air pipe.
Now that you are familiar with the function of the TAG system, it is time
to learn about the inspection and testing procedures used for this system.
31. The Air Valve Type air cleaner does not need a
acceleration.
motor to supply more air during cold
32. The Air Valve Type air cleaner will move to the
air mode during cold wide-open throttle acceleration.
-------
TAC
2-33
SYSTEM INSPECTION
A visual inspection of the TAC system should take place periodically and
previous to any testing. The visual inspection requires no tools or
instruments and takes only a few minutes. Many problems can easily be
avoided by following this simple procedure.
1. Check that the air cleaner is in place and has not been
modified.
The snorkel opening should not be blocked preventing air from
freely entering the system. Modifications to the air cleaner,
such as an upside down lid, shortened snorkel or holes drilled
into the air cleaner body will not allow the TAC system to
operate correctly.
2. Check that the air cleaner filter element is in place and clean.
A dirty filter element will decrease air flow to the carburetor
and possibly starve the engine of air.
3. Check the exhaust manifold heat shroud and hot air pipe
leading to the snorkel. They should be installed properly
and securely fastened.
These two components provide the path for heated air used in
the system. Connections must be secure to prevent loss of heat.
Passages must be open to allow proper flow of air.
4. Check the vacuum hose routing through the system.
Hose routings must be correct for the system to operate. The
routing must be followed from the vacuum motor into the air
cleaner and to the temperature sensor. This is accomplished
by si:u:;y r«,iiovi:i(j the air deo-rier winy n^t. and lifting off
-------
2-34
the top. From the temperature sensor the hose should connect
to the intake manifold where the vacuum signal is produced.
On systems equipped with a vacuum override motor, the vacuum
hose from the motor should be followed to the intake manifold
connection.
5. Check the vacuum hoses for cracks and deterioration.
Cracks and deterioration on vacuum hoses allow atmospheric
pressure to leak into the lines. This severely limits the
vacuum signal and prohibits proper system response.
6. Check that all hose connections are tight and secure.
A loose connection anywhere in the system will weaken or
prevent the vacuum signal from passing any further along the
routing.
33. When inspecting the TAG system, insure that the air
cleaner is properly in place and has not been
34. The opening should not be blocked
preventing air from freely entering the system.
35. All hose connections should be
-------
TAC
2-35
SYSTEM TESTING
The system should be tested periodically and whenever it is suspected
of working improperly. We have discussed the Thermostatic Type air
cleaner with and without the vacuum override motor. We have also examined
the Air Valve Type air cleaner. The testing procedures for each type will
now be presented.
THERMOSTATIC TYPE AIR CLEANER TEST
The Thermostatic Type air cleaner is relatively easy to test. First
inspect the air door linkage and spring for freedom of movement. If the
linkage and spring are functioning properly, remove the air cleaner
assembly from the carburetor. Lift off the air cleaner top and remove the
air cleaner assembly from carburetor. Place the snorkel, containing the
thermostat in a pan of water with a temperature below 85°F or place a cold
rag on the thermostat. Allow a few minutes for the assembly to reach this
TESTING HOT AIR MODE
OF THERMOSTAT
WATER TEMPERATURE
BELOW 85°F
FIGURE 2-20
cooler temperature. The thermostat should position the air valve door in
the heat on or hot air delivery mode.
-------
2-36
FIGURE 2-21
Now, using a thermometer and heat source, heat the water (or hot rag) to
approximately 130°F. At this temperature the thermostat should be fully
extended. This would position the air door in the cold air delivery mode,
allowing only cooler engine compartment air to enter the carburetor.
Should this cold air delivery mode not occur, the thermostat should be
replaced.
TESTING COLD AIR MOD
OF THERMOSTAT
WATER TEMPERATURE
ABOVE 130° F
FIGURE 3-22
-------
COLD AIR MODE
TAG
2-37
FIGURE 2-23
VACUUM OVERRIDE MOTOR TEST
If the system has a vacuum override motor, this component must also be
tested. With the engine off and the air cleaner assembly installed, cool
the thermostat to below 85°F. The air valve door should be in the
regulating mode position. If the air door is not in this position, check
for possible interference with the door opening or vacuum motor which
would not allow the door to move. Correct by realigning the air door or
vacuum motor as required. Next, with the temperature still below 85°F,
start the engine to introduce intake manifold vacuum to the override motor.
With temperature below 85°F the air valve door should be in the full hot
air delivery mode. Align the door or vacuum motor if interference is
noted. If the air valve door remains in the regulating mode position,
remove the vacuum hose at the override motor. Using a vacuum gauge check
for full manifold vacuum at the hose. If vacuum is weak, check for vacuum
leaks. If the vacuum signal is correct and the air valve door still will
not move, disconnect the vacuum motor and observe the action of the
thermostat on the air valve door. Using the testing procedure for the air
cleaner with the thermostat alone, determine if the air valve door moves
with temperature changes. If the thermostat operates the air door properly
without the vacuum motor, the problem is not in the thermostat or linkage
but with the vacuum motor itself.
-------
2-38
AIR VALVE TYPE AIR CLEANER TEST
We will now discuss the relatively easy testing procedures for the Air
Valve Type air cleaner. First a thermometer is taped in the air cleaner
next to the temperature sensor. Install a tee in the vacuum line between
vacuum motor and temperature sensor. Connect a vacuum gauge to the tee.
-VACUUM GAUGE
THERMOMETER
HOSE
TEE
TEMPERATURE
SENSOR
VACUUM
MOTOR
TO EXHAUST-
MANIFOLD
SHROUD
AIR,
CLEANER
TO CARBURETOR BASE
MANIFOLD VACUUM
FIGURE 2-24
ENGINE OFF
VACUUM MOTOR
TEMPERATURE
SENSOR
FIGURE 2-25
-------
TAG
2-39
With the engine off the air valve door should be closed to hot air, allow-
ing cold air to enter carburetor. This will occur at any temperature if
the engine is off. Look into the snorkel to make sure.
Either allow engine compartment to cool down or apply a cold wet rag or
ice to bring temperature down to 85°F or less. Start engine and allow it
to idle. The air valve door should be closed to engine compartment air.
The vacuum gauge should register full manifold vacuum.
A hand vacuum pump can also be used without starting the engine. If the
valve door is not closed with full vacuum at idle, shut off the engine and
check for the following:
ENGINE AT IDLE
VACUUM
GAUGE
VACUUM MOTOR
TEE
AIR FILTER
TEMPERATURE
SENSOR
HEATED
AIR
FIGURE 2-26
1. Binding air valve door. This is a common problem. Align
for free movement as necessary.
2. Disconnected linkage.
3. Vacuum leaks in the system (if full vacuum is not indicated on
vacuum gauge).
4. Defective vacuum motor.
-------
2-40
Next with the engine at idle (or vacuum created by hand pump) allow temp-
erature to rise above 85°F. As the temperature rises the air door should
begin to open to cooler engine compartment air.
WITH ENGINE AT IDLE 8 AMBIENT TEMPER-
ATURE BETWEEN 85° a 95° F, VALVE
DOOR SHOULD START TO OPEN.
00
oo
oo
r\ r\
FIGURE 2-27
Without a change in vacuum reading, the air door should be completely
opened to cold air at a temperature of approximately 130°F. If vacuum
reading drops to 5"-9" mercury (Hg) the temperature will be between 105°F
and 130°F when the door is completely opened.
When the air valve door in the snorkel begins to move toward the cold
air delivery mode, remove the cover on the air cleaner and check the
thermometer next to the sensor for specified temperature. Also check
vacuum reading. Vacuum reading should be 5"-9" of mercury (Hg) when the
air door is completely open to cold air. A hand vacuum pump with attached
gauge can also be used to conduct the vacuum test.
If the temperature is within specifications and the air valve door opens
to cold air, the system is operating correctly.
If the temperature is out of specifications, but vacuum is correct, "replace
the temperature sensor."
-------
TAG
2-41
TEMPERATURE
SENSOR
FIGURE 2-28
If both the temperature and vacuum are within specifications and the
air valve door remains closed to cooler engine compartment air, "replace
the vacuum motor." Remember: the temperature sensor is preset at the
factory, do not adjust.
Some manufacturers use an additional air intake that is available as an
option on certain models. The thermostatic controlled air cleaner is
basically the same as the air valve type discussed previously except it
has two snorkels.
One snorkel contains a vacuum motor with a temperature sensor and
works the same as we have discussed. The additional snorkel contains
a vacuum motor but does not have a temperature sensor. The air valve
door is controlled only by intake manifold vacuum and is closed to
cold air under all conditions except heavy acceleration. Testing
procedure is the same as for the single snorkel air cleaner.
-------
2-42
DUAL SNORKEL AIR
CLEANER
NON-
HEATED
AIR SNORKE
TO VACUUM
MOTOR
TO MANIFOLD VACUU
OPENING
TO EXHAUST
HEAT
SHROUD
TEMPERATURE
SENSOR
FIGURE 2-29
The processes and procedures above are basic to temperature controlled
air cleaners. For exact procedures and specifications on specific makes
and models you should refer to the manufacturer's technical and/or
service manual.
By following the inspection and servicing procedures for the TAG system,
the intake air for the carburetor will be approximately 100°F or higher.
This temperature enhances a more complete combustion, better cold engine
driveability and a significant reduction of HC and CO emissions.
36. First inspect the air
linkage and
spring for freedom of movement,
37. Place the snorkel, containing the
in a pan of water with a temperature below 85°F.
-------
TAG
2-43
38. Using a thermometer and heat source, heat the water (or
hot rags) to approximately 130°F. At this temperature,
the thermostat should be
39. During the vacuum override motor test, and if the thermo-
stat operates the air door properly without the vacuum
motor, the problem is not the thermostat or linkage but
with the itself.
-------
TAG
2-45
SYSTEM SUMMARY
PURPOSE
The TAG system is designed to provide heated air to the carburetor during
cold-engine conditions. By providing heated air during engine warm-up
conditions, a leaner air/fuel mixture can be used thereby reducing hydro-
carbon emissions. The system also assists in cold-engine driveabiltiy
and the elimination of carburetor icing.
MAIN COMPONENTS
Exhaust Manifold Heat Shroud - A metal shroud around the exhaust manifold
that directs air flow over the exhaust manifold to preheat it.
Hot Air Pipe - Directs air from the exhaust manifold heat shroud to the
snorkel of the air cleaner.
Air Door Assembly - Regulates when and how much heated air enters the air
cleaner.
Vacuum Diaphragm Unit - Controls the air door assembly. Actuated by
spring pressure and intake manifold vacuum.
Temperature Sensor - Senses incoming air temperature by means of a temp-
erature sensing spring. The position of the spring operates a small valve
that determines if vacuum is applied to vacuum diaphragm or if it is
vented.
SYSTEM FUNCTION
When the temperature sensor detects cold engine conditions, it allows
intake manifold vacuum to reach the vacuum diaphragm unit. When the
vacuum diaphragm receives a vacuum signal, it opens the air door assembly
to allow exhaust manifold heated air to enter system. As temperature of
incoming air reaches approximately 100°F, the temperature sensor bleeds
off vacuum to the diaphragm unit closing the system to heated air allow-
ing only cooler engine compartment air to enter.
-------
ANSWERS
TAG
2-47
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Thermostatic Air Cleaner
driveabiltiy
incomplete combustion
leaner
atomization
warm
heated air
warm-up
CO
Thermostatic
hot air
air valve
engine compartment
vacuum override
intake manifold
acceleration
air door
air bleed valve
temperature sensor
control or adjust
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
hot air mode
regulating mode
cold air mode
engine compartment
cold air mode
intake manifold
regulating mode
open
open
vacuum
vacuum override
cold
modified
snorkel
secure
valve door
thermostat
fully extended
vacuum motor
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 . REPORT NO.
EPA-450/3-77-037
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Motor Vehicle Emissions Control - Book Two
Thermostatic Air Cleaner Systems
5. REPORT DATE
November 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
B.D. Hayes
M.T. Maness
R.A. Ragazzi
R.A. Barrett
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Industrial Sciences
Colorado State University
Fort Collins, Colorado 80523
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
T008135-01-0
T900621-01-0
12. SPONSORING AGENCY NAME AND ADDRESS
Control Programs Development Division
Office of Air Quality Planning and Standards
Office of Air and Waste Management
U.S. Environmental Protection Agency
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA 200/04
15. SUPPLEMENTARY NOTES
Research Triangle Park, North Carolina 27711
16. ABSTRACT
This book is one of a series designed specifically to teach the concepts of auto-
mobile emissions control systems. It is intended to assist the practicing mechanic
or the home mechanic to better understand the Thermostatic Air Cl%aner Systems
which are an integral part of automobiles today. The mechanic's increased know-
ledge should help him keep "emissions controlled" vehicles operating as designed.
Respectable fuel economy, performance and driveability, as well as cleaner air, can
be obtained from the automobile engine that has all of its emissions systems
functioning properly.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Air Pollution
Thermostatic Air Cleaner
Photochemical
Hydrocarbons
Intake Manifold
System Inspection
Carbon Monoxide
Oxides of Nitrogen
13. DISTRIBUTION STATEMENT
Release Unlimited
Ignition Timing
Carburetion
Atomization
Acceleration
Temperature Sen
sor
Snorkel
Thermostat
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
54
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
*U.S. GOVERNMENT PRINTING OFFICE: 1978 -745-
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