OTHER Self Study Program 208 – Air Conditioner in the Motor Vehicle Fundamentals SSP-208-AC-in-the-motor-vehicle
Page 1
208
Service.
Self-Study Programme 208
Air Conditioner in the Motor Vehicle
Fundamentals
1,6
1,4
1,2
MPa
1,0
0,8
0,6
Pressure
0,4
0,2
0
-30
Temperature
-10-20
0
o
C
10 20
30
40 50
60
70
Page 2
airair
conditioncondition
Air conditioning systems have long ceased to be
regarded as luxury equipment.
Air conditioners have become a factor in active
safety, and today can almost be considered as
an integral part of a vehicle's safety
specification.
10 years ago, only about 10 percent of
all newly registered vehicles were fitted with an
air conditioning system. By 1996, air conditioners
were being installed as standard in more than
one in four newly registered vehicles.
Customer demand for air conditioning is rising
continually.
The design of the refrigerant circuit of an
air conditioner is identical in all vehicles.
Air conditioner refrigerant circuits only vary in
respect of how they are adapted to meet
refrigeration requirements.
In this Self-Study Programme, you will familiarise
yourself with the basic purpose and design of an
air conditioner.
You will learn the functions of the component
parts in the refrigeration process, the special
characteristics of the refrigerant and why air
conditioners require special service
specifications.
The component parts shown in the following SSP
are common to most air conditioners.
Please note that the figures specified
are given by way of example only.
Depending on refrigeration requirements, the
absolute values vary from vehicle to vehicle.
The Self-Study Programme
is not a Workshop Manual!
2
New Important
Note
Please always refer to the relevant Service Literature
for all inspection, adjustment and repair instructions.
Service literature.
Page 3
Table of Contents
The in-car climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Why air conditioning?
The physics of the cooling system . . . . . . . . . . . . . . . . . . . . . . . . 6
Applied physics
The refrigerant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
The cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
The principle of the refrigerant circuit
Refrigerant circuit with expansion valve
The compressor
The mode of operation of the compressor
Magnetic clutch
The condenser
The fluid container and drier
Expansion valve
Expansion valve – new generation
The evaporator
Refrigerant circuit with restrictor
The restrictor
The collecting tank
System control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Components of the safety system
Cooling fan circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Fan circuit for engine/condenser cooling
Radiator fan control unit J293
MPa
o
R
134a
p
t°
C
Temperature control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Manual control
Automatic control
System overview
Control unit with operating and display unit
The main temperature sensors
Auxiliary signals for temperature control
Positioning motor
Air ducting
Air distribution
Air recirculation mode
Technical service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Safety precautions
General information on function influencing factors
Fault diagnosis through pressure testing
Fault diagnosis through self-diagnosis
Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Key cooling system terminology
3
Page 4
The in-car climate
Why air conditioning?
People feel comfortable at a certain ambient
temperature and atmospheric humidity.
As a component part of active safety, the driver's
well-being is a key factor in driving ability.
The “in-car climate“ has a direct bearing on the
driver, fatigue-free driving and driving safety.
A comfortable interior temperature is dependent
upon the prevailing ambient temperature and
upon sufficient air flow:
Low ambient temperature, e.g. –20
Higher interior temperature 28
High air flow rate: 8 kg per min.
High ambient temperature, e.g. 40
Low interior temperature 23
High air flow rate: 10 kg per min.
Moderate ambient temperature, e.g. 10
Low interior temperature 21.5
Low air flow rate: 4 kg per min.
– In strong sunlight in particular, the heated
cabin air can only be exchanged for air with
ambient temperature.
– In addition, the air temperature usually rises
en route from the intake point to the air outlet.
– Opening a window or sliding roof or setting a
higher fan speed for greater comfort will
usually result in a draught and expose the
occupants to other nuisances such as noise,
exhaust gases and pollen.
o
C
o
C
°
C
o
C
o
C
o
C
o
C
28
26
24
Interior temperature
22
Comfort curves
kg/min
8
6
4
2
Air flow rate
Even modern heating and ventilation systems
have difficulty maintaining a pleasant climate
inside a vehicle at high ambient temperatures.
20
10
20
-20
-10
0
Ambient temperature
30 40
0
°
C
208_043
Why?
High levels of atmospheric humidity put the body
under considerably greater physical strain.
Temperatures in a mid-range passenger car
where: driving time 1 h
ambient temperature 30
sunlight penetration into car
Area
Head
Chest
Feet
o
C
with
air conditioning
23 °C
24 °C
28 °C
without
air conditioning
42 °C
40 °C
35 °C
208_001
4
Page 5
Effects of an unfavourable vehicle interior
temperature on humans
Scientific studies conducted by the WHO (World
Health Organization) have shown that one's
ability to concentrate and reactions are impaired
when under stress.
Heat puts a strain on the body.
Comfort range
A B C
Transpiration
The best temperature for the driver is between
20 and 22
o
C.
This is equivalent to climatic load A, the "comfort
range".
Strong sunlight can increase the interior
temperature by more than 15
o
C above the
ambient temperature– particularly in the head
area.
This is where the effects of heat are most
dangerous.
The body temperature rises and the heart rate
increases.
Heavier perspiration will typically occur, too.
The brain is not receiving enough oxygen.
Also refer to "climatic load range B".
Climatic loads in range C put an excessive strain
on the body.
Physicians specialising in traffic-related illnesses
refer to this condition as “climatic stress“.
Studies have shown that an increase in
temperature from 25 to 35
o
C reduces one's
sensory perception and powers of reasoning by
20%. It has been estimated that this figure is
equivalent to a blood alcohol concentration of
0.5 millilitres alcohol level.
Heart
Strain
rate
Body temperature
Climatic load
highmoderatelow
208_042
The air conditioner - a system which keeps the air
temperature at a level comfortable to humans,
as well as purifying and dehumidifying the air -–
was created in order to reduce or eliminate
completely such stress.
With the help of an air conditioner it is possible
to produce at the air outlets a temperature which
is much lower than high outside air
temperatures.
This is possible both when the vehicle is at a
standstill and when it is in operation.
A technical side-effect of air conditioning is that
the air is dehumidified and cleaned at the same
time. However, this is just as important as the
reduction in temperature.
The pollen filter and activated charcoal filter also
help to clean the air entering the vehicle.
People with allergic illnesses benefit greatly from
being able to breathe clean air.
In-vehicle air conditioning is
- a real safety element
- a functional accessory not only for expensive tastes
5
Page 6
MPa
Physics of the cooling system
Applied physics
Laws
o
C
Many substances are known to exist in three
aggregate states.
Ice – solid
Take water for example: solid – liquid – vapour.
The principle of cooling follows this law.
Even in ancient times there was a need for
cooling. One of the first methods used to cool
foodstuffs was to store them in an “icebox“.
The ice (water in a solid aggregate state)
absorbs the heat of the foodstuffs, thereby
cooling them down.
The ice melts as a result, assuming another
aggregate state, namely that of a liquid (water).
If the water is heated further, it will boil and
evaporate.
The water is now in the gaseous state.
The gaseous substance can be converted back to
a liquid by cooling it and will become a solid
again if cooled further.
This principle is applicable to almost all
substances:
208_039
Ice – becomes
a liquid when it absorbs
heat
208_040
A
Water – becomes
E
S
a gas when it absorbs heat
208_041
– A substance absorbs heat when it is conver-
ted from a liquid to a gas.
Law
– A substance gives off heat when it is conver-
ted from a gas to a liquid.
– Heat always flows from the warmer substance
to the colder substance.
Air conditioners utilise the effects of heat
exchange, a process in which a substance
Freezing point,
e.g. water becomes ice,
Boiling point
e.g. water becomes steam
changes state at certain points.
6
Page 7
PPPPrrrreeeessssssssuuuurrrreeee aaaannnndddd bbbbooooiiiilllliiiinnnngggg ppppooooiiiinnnntt
tt
If the pressure is changed using a liquid, the
boiling point changes.
All liquids behave similarly.
Boiling point H
O/water = 100
2
Machine oil = 380 - 400
The lower the pressure, the lower the
temperature at which water boils (evaporates).
Vapour pressure curve
O
H
2
1,7
1,5
17
15
The evaporation process is also used in vehicle
air conditioners.
MPa
A substance with a low boiling point is used for
o
o
C
o
C
This substance is known as a refrigerant.
Boiling point Refrigerant R12 –29.8
Refrigerant R134a –26.5
o
C
o
C
this purpose.
C
(The boiling points specified for liquids in the
table always refer to an atmospheric pressure of
0.1 MPa = 1 bar.)
Vapour pressure curve
R134a R12
4,0
3,5
40
35
1,3
MPa
1,1
Liquid
0,9
0,7
Pressure
0,5
Gaseous
0,3
0,1
100
110 120130 140 150 160 170 180 190 200
Temperature
What does a vapour pressure curve tell us?
We can draw the following conclusions from the vapour
pressure curve for the two refrigerants R134a and R12
(R12 is no longer used) and water:
°C
13
bar
11
9
7
5
3
1
208_006 208_005
3,0
MPa
2,5
Liquid
2,0
1,5
Pressure
1,0
Gaseous
0,5
0
-40 -20 0 20 40 60 80 100
Temperature
°C
30
25
20
15
10
5
0
bar
– At a constant pressure, the vapours become a liquid
through temperature reduction (in the air conditioner
circuit, this process takes place in the condenser =
liquefier),
– The refrigerant goes from a liquid state to a vapour
state through pressure reduction (in the air conditioner
circuit, this process takes place in the evaporator).
7
Page 8
The refrigerant
R
134a
The refrigerant with a low boiling point used
for vehicle air conditioners is a gas.
As a gas, it is invisible.
As a vapour and as a liquid, it is colourless like
water.
Refrigerants may not be combined with each
other. Only the refrigerant specified for the
system in question may be used.
With regard to vehicle air conditioners, the sale
and filling of refrigerant R12 were banned in
Germany with effect from 1995 and July 1998
respectively.
In current automotive air conditioners, only
refrigerant R134a is used.
Refrigerant RRRR111122
chem. formula CCl
22
– Dichlordifluormethane
F
2
2
a chlorinated hydrocarbon ( CCCCFFFFCC
harmful to the environment!
Refrigerant RRRR111133334444aa
chem. formula CH
a fluorocarbon ( FFFFCC
aa
– Tetrafluorethane
F-CF
2
3
CC
)
environmentally friendly!
Ordinance banning halogens
CC
)
– R134a – a fluorocarbon contains no chlorine
atoms - unlike refrigerant R12 - which cause
depletion of the ozone layer in the earth's
atmosphere when they split.
– The vapour pressure curves of R134a and R12
are very similar.
R134a has the same refrigeration capacity as
R12.
It is possible to adapt air conditioners which
now may no longer be filled with R12 to R134a
with a special conversion kit
(Retrofit method).
The systems converted in this way are no longer able to match their original refrigeration
capacity.
Depending on the pressure and temperature
conditions in the refrigerant circuit, the
refrigerant will either be a gas or a liquid.
bar
Pressure
16
14
12
10
R134a
Liquid
Expansion
8
6
4
2
0
-30
0
-10-20
Temperature
10 20
Evaporation
Gaseous
40
30
50 60
70
o
C
Vapour pressure curve of R134a
208_050
8
Page 9
State of refrigerant R134a
in the cycle in an air conditioner
In addition to the vapour pressure curve, the
cycle shows the change of state of the refrigerant
under pressure and temperature in addition to
the energy balance at which the refrigerant
returns to its original state.
The diagram is an excerpt from the state
diagram of refrigerant R134a for a vehicle air
conditioner.
Different absolute values are possible in
dependence upon the demand of a vehicle type
for refrigeration capacity.
Temperature curve
Saturated liquid
4,0
MPa
2,0
1,6
1,0
0,8
0,6
Pressure
20
C
40
30
The energy content is a key factor in the design
of an air conditioner.
It shows what energy is required (evaporator
heat, condenser heat) to achieve the intended
refrigeration capacity.
Physical data of R134a:
R
Boiling point: –26.5 °C
Freezing point: –101.6 °C
Critical temperature: 100.6 °C
Critical pressure: 4.056 MPa
(40.56 bar)
Critical point
(pressure/temperature)
90
80
70
60
50
30
20
Temperature curve
Saturated vapour
90
85
80
70
60
50
40
40
bar
20
16
B
10
8
6
Pressure
134a
0,4
0,3
10
C
0
D
0,2
200 240 280 320 360 400 440
Energy content
kJ/kg
10
C
0
A
4
3
2
208_053
A B Compression in the compressor, pressure and temperature rise,
gaseous, high pressure, high temperature
B C Condensation process in the condenser, high pressure, temperature reduction,
the liquid leaves the condenser slightly cooled
C D Expansion = sudden pressure relief, results in evaporation
D A Evaporation process (heat absorption) in the evaporator.
Transition path from vapour state to gaseous state (low pressure)
Temperature curve at point B
For a glossary refer to page 72.
9
Page 10
R
134a
The refrigerant
Refrigerants and ozone layer
Ozone protects the earth's surface against
UV radiation by absorbing a large proportion of
these rays.
UV rays split ozone (O
molecule (O
) and in an oxygen atom (O).
2
Oxygen atoms and oxygen molecules from other
reactions combine again to form ozone.
This process takes place in the ozonosphere, a
part of the stratosphere at an altitude of between
20 and 50 km.
Like R12, chlorine (Cl) is a constituent of a CFC
refrigerant .
If handled improperly, the R12 molecule will rise
up to the ozone layer– since it is lighter than air–.
) into an oxygen
3
UV
+
Cl
FCKW
UV
km
UV
200
100
80
60
S
O
P
H
T
A
R
T
S
Ä
40
=
O
3
20
10
S
P
H
O
P
Ä
O
R
T
R
5
1
UV
R
E
ClO
O
2
E
FCKW
Global warming
UV
Cl
O
UV radiation liberates a chlorine atom in the
CFC, and this atom reacts with the ozone.
In the process, the ozone decomposes leaving an
oxygen molecule (O
(ClO), which then reacts again with oxygen and
liberates chlorine (Cl). This cycle can repeat itself
as many as 100,000 times.
However, free oxygen molecules (O2) cannot
absorb UV radiation.
Refrigerants and global warming
The sunlight impinging upon the earth's surface
is reflected in the form of infrared radiation.
However, trace gases – most importantly CO
reflect these waves in the troposphere.
This causes the earth's atmosphere to heat up,– a
phenomenon which is commonly referred to as
"global warming". CFCs are heavily responsible
for the increasing trace gas concentration.
1 kg of R12 has the same greenhouse effect
as 4000 tons of CO
R134a only makes a small contribution
to global warming.
Its ozone depletion potential is nil.
) and chlorine monoxide
2
.
2
208_051
Reaction between CFC and
ozone in the atmosphere
(CFC = FCKW)
–
2
FCKW
R12
1
FKW
R134a
0
Ozone depletion potential
0
1
2
Greenhouse potential
3
4
208_052
10
Page 11
Refrigerant oil
A special oil – the refrigerant oil – free of
impurities such as sulphur, wax and moisture is
required to lubricate all the movable parts in the
air conditioner.
The refrigerant oil must be compatible with the
refrigerant itself, because some of the refrigerant
oil mixes with the refrigerant in the refrigerant
circuit. In addition, the refrigerant oil must not
attack the seals used in the system.
No other oils may be used, as they lead to
copper plating, the build-up of carbon deposits
and the formation of residues which can cause
premature wear and irreparable damage to
movable parts.
A special synthetic oil is used for the R134a
refrigerant circuit. This oil may only be used for
this particular refrigerant, since it does not mix
with other refrigerants.
Compressor
50%
10%
10%
Condenser
Fluid container
Distribution of oil quantity in the refrigerant circuit
(roughly)
The filling quantity of refrigerant varies according to
the design of the units used in a particular type of
vehicle.
20%
10%
Evaporator
R
134a
Suction hose
Also, the refrigerant oil can only be adapted to a
specific compressor type.
The refrigerant for R134a
Designation: PPPPAAAAGG
Properties:
- high solubility in combination with
refrigerant
- good lubrication properties
- acid free
- highly hygroscopic (water-attracting)
- cannot be mixed with other oils
N.B.:
- must not in be used in older refrigeration
systems
filled with refrigerant R12,
since it is incompatible with R12
GG
= Polyalkylene glycol
Important notes:
– Do not store in the open (highly hygroscopic).
– Always keep oil tanks closed to protect them
against the ingress of moisture. Close opened
drums immediately.
– Do not use old refrigerant.
– DDDDiiiissssppppoooosssseeee ooooffff aaaassss ttttooooxxxxiiiicccc wwwwaaaasssstttteeee..
Refrigerant may not be disposed of together
with engine oil or gear oil because of its che-
mical properties.
..
11
Page 12
The cooling system
The principle of the refrigerant circuit
The cooling process and the technical conditions
We know that:
Too cool down an object, heat must be given off.
A compression refrigeration system is used in
motor vehicles for this purpose. A refrigerant
circulates in the closed circuit, continually
alternating changing from a liquid to a gas and
vice versa. The refrigerant is:
– compressed in the gaseous state,
– condensed through heat dissipation
– and evaporated through pressure reduction
and heat absorption.
Cool air is not produced, heat is
extracted from the air flow in the vehicle.
How does this process work?
The ccccoooommmmpppprrrreeeessssssssoooorrrr induces cold, gaseous
refrigerant at a low pressure.
Low-pressure side
High-pressure side
Compressor
208_071
12
The refrigerant is compressed in the
compressor, causing it to heat up.
The refrigerant is pumped into the circuit on
the high-pressure side.
In this phase, the refrigerant
is in a gaseous state,
has a high pressure and
a high temperature.
Cooling air
Condenser
Page 13
Valve
Cooled fresh air
Evaporator
208_004
208_073
The compressed liquid refrigerant continues to
flow up to a narrowing. This narrowing can be in
the form of a restrictor or an expansion valve.
Once the refrigerant reaches the narrowing, it is
injected into the evaporator causing its pressure
to drop (low-pressure side).
Inside the eeeevvvvaaaappppoooorrrraaaattttoooorrrr, the injected liquid
refrigerant expands and evaporates. The
evaporation heat required for this purpose is
extracted from warm fresh air which cools down
when it passes through the evaporator fins.
The temperature inside the vehicle is reduced to
a pleasant level.
In this phase, the refrigerant
is in a vapour state,
under low pressure and
at low temperature.
Warm fresh air
208_072 208_074
The refrigerant follows the short path to the
ccccoooonnnnddddeeeennnnsssseeeerrrr (liquefier).
Heat is now extracted from the compressed, hot
gas in the condenser by the air flowing through
(headwind and fresh air blower).
The refrigerant condenses and becomes a liquid
when it reaches its melting point (pressuredependent).
In this phase, the refrigerant
is therefore
in a liquid state,
has a high pressure
and a medium temperature.
Now in the gaseous state again, the refrigerant
emerges from the evaporator.
The refrigerant is again drawn in by the compressor
and passes through the cycle once again.
Thus, the circuit is closed.
In this phase, the refrigerant
is again
gaseous,
has a low pressure
and a low temperature.
13
Page 14
The cooling system
Refrigerant circuit with expansion valve
I
ND
HD
A B C D E F
H
G
1
Working pressure HD = High-pressure
ND = Low pressure
In technical documents such as Workshop
Manuals, the components are represented in a
diagrammatic form.
ND
HD
208_032
H
I
E
D
The refrigerant circuit is activated
when the vehicle engine is
running. For this purpose, the
compressor has a magnetic
clutch.
1 MPa = 10 bar
The absolute values are
always vehiclespecific.
Please observe the
Workshop Manual.
Pressures and
temperature in
the circuit
14
(example)
A
B
CCCCoooommmmpppprrrreeeessssssssiiiioooonnnn rrrraaaattttiiiioo
at approx. 1.4 MPa (14 bar)
Temperature approx. 65
oo
o
2
C
21
CCCCoooonnnnddddeeeennnnssssaaaattttiiiioooonn
Pressure approx. 1.4 MPa (14 bar)
C
Temperature reduction: 10
nn
o
C
Page 15
Legend
The components:
High pressure
Low pressure
3
F
G
4
A Compressor with magnetic clutch
B Condenser
C Fluid container with drier
D High-pressure switch
E High-pressure service connection
F Expansion valve
G Evaporator
H Low-pressure service connection
I Damper (vehicle-specific)
The refrigerant circuit may not be
opened for safety reasons.
If it is necessary to open the
refrigerant circuit in order to
perform repair work on the
vehicle, the refrigerant must be
drawn off beforehand using a
suitable service station.
The refrigeration capacity of a vehicle air
conditioner is dependent upon the car-specific
installation conditions and the vehicle category
(passenger cars, vans).
The components A to H exist in every circuit.
Additional connections can be provided for
service work, temperature sensors, pressure
switches in the high- and low-pressure circuit and
oil drain screws depending on the circuit design
and requirements. The layout of components
within the circuit also differs from one vehicle
type to another.
Some systems have a damper before the
compressor in order to dampen refrigerant
vibrations.
3
208_031
The pressures and temperatures in the circuit are
always dependent on momentary operating
state. The specified values are intended as a
rough guideline only. They are reached after
20 min. at an ambient temperature of 20
at engine speeds of between 1500 and 2000
rpm.
o
At 20
pressure of 0.47 MPa (4.7 bar) will build up
inside the refrigerant circuit.
The components of the refrigerant circuit with
expansion valve will now be examined more
closely (for details of the refrigerant circuit with
restrictor refer to page 28).
C and when the engine is at a standstill, a
4
o
C and
1
EEEExxxxppppaaaannnnssssiiiioooonn
from approx. 1.4 MPa (14 bar) to approx. 0.12 MPa
(1.2 bar), Temperature: from approx. 55
nn
o
C to –7 oC
EEEEvvvvaaaappppoooorrrraaaattttiiiioooonn
Pressure: approx. 0.12 MPa (1.2 bar)
Temperature: approx. –7
nn
o
C
208_033
15
Page 16
The cooling system
The compressor
The compressors used in vehicle air conditioners
are oil-lubricated displacement compressors.
They operate only when the air conditioner is
switched on, and this is controlled by means of a
magnetic clutch.
The compressor increases the pressure of the
refrigerant. The temperature of the refrigerant
rises at the same time.
Were there to be no pressure increase, it would
not be possible for the refrigerant in the air
conditioner to expand and therefore cool down
subsequently.
A special refrigerant oil is used for lubricating
the compressor. About half of it remains in the
compressor while the other half is circulated with
the refrigerant.
A pressure shut-off valve, which is usually
attached to the compressor, protects the system
against excessively high pressures.
208_028
The compression process
The compressor draws in cold, gaseous
refrigerant through the evaporator under low
pressure .
It is "vital" for the compressor that the
refrigerant be in a gaseous state, because liquid
refrigerant cannot be compressed and would
destroy the compressor (in much the same way
as a water shock can damage an engine).
The compressor compresses the refrigerant and
forces it towards the condenser as a hot gas on
the high-pressure side of refrigerant circuit.
The compressor therefore represents the
interface between the low-pressure and highpressure sides of the refrigerant circuit.
Compressor
208_045
Magnetic clutch
16
Page 17
Mode of operation of compressor
Compressors for air conditioners operate
according to various principles:
– Reciprocating compressors
– Coiled tube compressors
– Vane-cell compressors
– Wobbleplate compressors
Wobbleplate compressors will now be examined
in more detail.
The turning motion of the input shaft is converted
to an axial motion (= piston stroke) by means of
the wobbleplate.
Depending on compressor type, between 3 and
10 pistons can be centred around the input shaft.
A suction/pressure valve is assigned to each
piston.
These valves open/close automatically in rhythm
with the working stroke.
An air conditioner is rated for the max. speed of
the compressor.
However, the compressor output is dependent on
engine rpm.
Compressor rpm differences of between 0 and
6000 rpm can occur.
This affects evaporator filling as well as
the cooling capacity of the air conditioner.
Controlled-output compressors with a variable
displacement were developed in order to adapt
compressor output to different engine speeds,
ambient temperatures or driver-selected interior
temperatures.
Input shaft
Wobbleplate
Wobbleplate compressor (non-self-regulating)
Angle of wobbleplate constant
Displacement constant
208_027
Suction/
pressure
valve
Piston
Compressor output is adapted by adjusting the
angle of the wobbleplate.
In constant-displacement compressors,
compressor output is adapted to the demand for
refrigeration by switching the compressor on and
off periodically via the magnetic clutch.
Piston
Wobbleplate compressor (self-regulating)
Angle of wobbleplate variable
Displacement variable
Wobbleplate
208_046
17
Page 18
The cooling system
The self-regulating compressor
runs continously in air condition mode
Control range of compressor
All control positions between upper stop (100 %)
and the lower stop (approx. 5 %) are adapted to the required delivery rate
by altering the chamber pressure.
The compressor is on continuous duty during the control cycle!
Calibrated
restrictor bore
High pressure
Low pressure
Regulating valve
Upper side
Piston
Lower side
Wobbleplate
Chamber pressure
Springs
Slide rail
Input shaft
208_047
Drive hub
18
The turning motion of the input shaft is
transmitted to the drive hub and converted to
axial motion of the piston via the wobbleplate.
The wobbleplate is located longitudinally in a
slide rail.
The piston stroke and the delivery rate are
defined by the inclination of the wobbleplate.
IIIInnnncccclllliiiinnnnaaaattttiiiioooonnnn – dependent on the chamber
pressure and hence the pressure conditions at
the base and top of the piston.
The inclination is supported by springs located
before and after the wobbleplate.
CCCChhhhaaaammmmbbbbeeeerrrr pppprrrreeeessssssssuuuurrrreeee – is dependent upon the
high and low pressures acting upon the
regulating valve and by the calibrated restrictor
bore.
High pressure, low pressure and chamber
pressure are equal when the air conditioner is
off.
The springs before and after the wobbleplate set
it to a delivery rate of about 40%.
The advantage of output control is
that it eliminates compressor cut-in shock, which
often manifests itself in a jolt while driving.
Page 19
High delivery rate for high cooling capacity - low chamber pressure
Regulating valve
Restrictor bore
Bellows 2
Bellows 1
Chamber pressure
Chamber pressure
Spring 1
High pressure
The high and low pressures are relatively high.
– Bellows 2 is compressed by the high pressure .
– Bellows 1 is also compressed by the relatively
high low pressure.
– Regulating valve opens. Chamber pressure is
reduced via the low-pressure side.
208_048
Spring 2
Low pressure
– The combined force resulting from the low
pressure acting upon the upper sides of the
piston and the force of spring 1 is greater than
the combined force resulting from the chamber pressure acting upon the lower sides of
the piston and the force of spring 2.
Inclination of wobbleplate
increases
= large stroke with high delivery rate
19
Page 20
The cooling system
Low delivery rate and low cooling capacity - high chamber pressure
Regulating valve
Restrictor bore
Bellows 2
Bellows 1
Chamber pressure
Chamber pressure
The high and low pressures are relatively low.
– Bellows 2 opens out.
– Bellows 1 also opens out as a result of the
relatively low pressure.
– Regulating valve closes.
The low-pressure side is closed against the
chamber pressure.
– Chamber pressure rises via the calibrated
restrictor bore.
Spring 1
High pressure
Spring 2
Low pressure
– The combined force resulting from the low
pressure acting upon the upper side of the
piston and the force of spring is greater than
the combined force resulting from the chamber pressure acting upon the lower sides of
the piston plus the force of spring 2.
Inclination of wobbleplate
decreases
= small stroke with low delivery rate.
208_049
20
Page 21
Magnetic clutch
Schematic diagram of clutch switched off
The drivetrain is connected between the
compressor and vehicle engine while the engine
is running by means of the magnetic clutch.
Design
The clutch comprises
– Belt pulley with bearing
– Spring plate with hub
– Magnetic coil
The hub of the spring plate is permanently
mounted the compressor input shaft. The belt
pulley is mounted in a pivot bearing on the
housing of the compressor at the shaft output.
The magnetic coil is permanently connected to
the compressor housing. There is an open space
“A“ between the spring plate and the belt pulley.
Spring plate
with hub
Magnetic coil
A
Belt pulley with bearing
Compressor
Input shaft
Compressor
housing,
208_002
Function
The vehicle engine drives the belt pulley (Arrow)
by means of the ribbed V-belt.
The belt pulley follows on freely when the
compressor is switched off.
When the compressor is connected, voltage is
present at the magnetic coil. A magnetic force
field is created. This force field draws the spring
plate towards the rotating belt pulley (the open
space “A“ is bridged) and makes a positive
connection between the belt pulley and the input
shaft of the compressor.
The compressor runs on.
The compressor runs on until the electrical circuit
to the magnetic coil is opened.
The spring plate is then retracted by the belt
pulley by means of springs.
The belt pulley again runs without driving the
compressor shaft.
Schematic diagram of clutch switched on
Force flow
208_003
For compressor switch-on and switch-off
conditions– refer to Air conditioning
function control.
21
Page 22
The cooling system
The condenser
The condenser is the “cooler“ of the air
conditioner.
Design of condenser
The condenser comprises a tube coil which is
securely attached to fins creating a large cooling
surface which facilitates heat transfer.
The condenser cooled by the cooling fan after
the air conditioner is switched on in order to
ensure that the refrigerant is circulated. The
condenser is always installed upstream of the
cooler.
This increases the efficiency of the condenser.
208_023
Heat is exchanged in the condenser through air
cooling. The air is cooled by the headwind and
by the cooling fan – an auxiliary fan may still be
in use depending on type. The fan usually starts
up when the air conditioner is switched on. This is
not the case if pressure sender G65 is fitted; in
this case, fan switch-on will then be delayed until
a specific pressure is reached.
Impurities in the condenser reduce air flow and
can also impair condenser capacity and engine
cooling.
Function of condenser
Hot, gaseous refrigerant coming from the
compressor at a temperature of approx. 50 -
o
70
C is injected into the compressor.
The tubes and fins of the condenser absorb
heat.
Cool ambient air is ducted over the condenser,
absorbing heat in the process and thereby
cooling down the refrigerant.
When the refrigerant cools down, it condenses
at a specific temperature and pressure and
becomes a liquid. At the bottom of the
compressor, the refrigerant emerges from the
condenser as a liquid.
Ambient air, cool
The condenser is often referred to as
“liquefier“ in regard to its working
method.
Condenser
Cooling fan
Cooler
Ambient air,
heated
Hot,
gaseous
refrigerant
Liquid
refrigerant
208_024
22
Page 23
The fluid container and drier
In the refrigerant circuit with expansion valve, the
fluid container serves as a refrigerant expansion
tank and reservoir.
Different amounts of refrigerant are pumped
through the circuit when operating conditions
such as the thermal load on the evaporator and
condenser and compressor rpm are variable.
The fluid container is integrated in the circuit in
order to compensate for these fluctuations.
The drier binds chemically moisture which has
entered the refrigerant circuit during installation.
The drier can absorb between 6 and 12 g of
water, depending on type. The amount of water
that can be absorbed is temperature-dependent.
The amount of water absorbed increases as the
temperature drops. Abraded material from the
compressor, dirt arising from installation work
and similar is also deposited.
208_026
To
expansion valve
Function
The liquid refrigerant coming from the condenser
enters the container at the side. The refrigerant is
collected in the container, then it flows through
the drier and along the riser to the expansion
valve in an uninterrupted flow containing no
bubbles.
The fluid container is replaced every
time the refrigerant circuit is opened.
The fluid container must be kept closed
as long as possible prior to installation
in order to minimise absorption of
moisture from the ambient air in the
drier.
From
condenser
Drier
208_025
Filter
strainer
23
Page 24
The cooling system
Expansion valve
The expansion valve is the point where the
refrigerant in the evaporator expands and cools
down. It forms the interface between the highpressure side and low-pressure side of the
refrigerant circuit.
The expansion valve is used to regulate the
refrigerant flow to the evaporator – in
dependence upon the temperature of the
refrigerant vapour at the evaporator outlet.–
No more refrigerant than is necessary to
maintain a steady “refrigerating climate“ in the
evaporator is expanded in the evaporator.
The closed control loop
The refrigerant flow is controlled by the
expansion valve in dependence upon
temperature.
– When the temperature of the refrigerant
leaving the evaporator rises, the refrigerant in
the thermostat expands. The flow rate of the
refrigerant to the evaporator at the globe
valve increases.
– When the temperature of the refrigerant
leaving the evaporator drops, the refrigerant
volume in the thermostat decreases. The flow
rate to the evaporator at the globe valve is
reduced.
There are three forces at play in the thermostatic
expansion valve:
1. The pressure in the sensor line is dependent
on the temperature of the superheated
refrigerant. This pressures acts upon the
membrane as an opening force (P
Fü
208_022
Thermostat with sensor line
and refrigerant
P
Fü
Membranes
To compressor (low
pressure)
From condenser
(high pressure)
Globe valve
Regulating spring
P
Sa
From evaporator
(low pressure)
To evaporator
(low pressure)
P
Fe
208_015
).
24
2. The evaporator pressure (P
) acts upon
Sa
the membrane in the opposite direction.
3. The pressure exerted by the regulating
spring (P
) acts in the same direction as the
Fe
evaporator pressure.
The expansion valves are set.
Their settings may not be altered.
Do not bend the sensor line, because it
is filled with a special gas.
Page 25
Expansion valve – new generation
This expansion valve is also positioned between
the high-pressure side and low-pressure side of
the refrigerant circuit directly upstream of the
evaporator.
To compressor
(low pressure)
Thermal head with
special gas filling
Pressure-equalising
hole
From condenser
(high pressure)
Regulating spring
The expansion valve is heat-controlled. It has a
control unit with a thermal head and a globe
valve.
The thermal head on one side of the membrane
has a special gas filling. The other side is
connected to the evaporator outlet (low pressure)
via pressure-equalising holes.
The globe valve is push rod actuated.
The pressure of the special gas, and therefore
also the amount of refrigerant injected, is
dependent upon the temperature on the lowpressure side.
Evaporator outlet
(low pressure)
Membranes
Push rod
To evaporator
(low pressure)
208_017
Globe valve
The expansion valve is always fitted with thermal
insulation.
Fitting the valve without thermal
insulation will alter the set control
characteristic.
25
Page 26
The cooling system
A increase in cooling load increases the
temperature at the evaporator outlet
causing
the pressure (p
thermal head to rise
) of the gas filling in
a
p
a
The globe valve cross-section is
via diaphragms and the push rod.
Refrigerant flows to evaporator and
absorbs heat at the transition from high
pressure to low pressure
Heat is extracted from the air flowing
through the evaporator
When the temperature of the
refrigerant at the evaporator outlet
pressure (p
b
enlarged
drops, the
) in the thermal head drops
208_018
208_019
p
b
208_020
26
The cross-section of the globe valve,
and therefore also the flow rate to
evaporator, will again be reduced.
208_021
The valve opening ratio is dependent upon the
temperature at the evaporator outlet (low
pressure).
Pressure equalisation is controlled.
Page 27
The evaporator
The evaporator operates according to the same
principle as a heat exchanger.
It is an integral part of the air conditioner in the
heater box. When the air conditioner is switched
on, heat is extracted from the air which flows
through the fins of the cold evaporator. This air is
cooled, dried and cleaned in the process.
Refrigerant return
line (gaseous state)
Refrigerant supply
line (vapour state)
Tubular evaporator
Function
The refrigerant released by the expansion valve
expands in the evaporator, cooling the
evaporator down considerably.
The refrigerant becomes a gas (boiling point).
When the refrigerant in the evaporator boils, the
temperatures are well below the freezing point
of water.
The refrigerant extracts the heat required for
evaporation from its surroundings – which is the
air flowing through the evaporator in this case.
208_029
208_030
Moisture in the cooled air collects at the
evaporator in the places where the air
temperature drops below the dewpoint
temperature, i.e. it condenses. Condensation
water is produced.
The air is “dried“.
This improves the climate and air quality inside
the vehicle noticeably.
Deposits of matter suspended in the air build up
at the evaporator in addition to moisture.
The evaporator also "purifies" the air.
This air is channeled into the passenger cabin in
a “cooled" state.
Pools of water below a stationary
vehicle (condensation) are therefore not
an indication of a fault.
27
Page 28
The cooling system
Refrigerant circuit with restrictor
FGHI
ND
HD
A B C D
1
E
208_034
Working pressure HD = high pressure
ND = low pressure
Schematic diagram of a refrigerant circuit with
restrictor
H
I
1 MPa = 10 bar
Pressures and
temperatures
in the circuit
28
A
B
CCCCoooommmmpppprrrreeeessssssssiiiioooonnnn rrrraaaattttiiiioo
Max. pressure 2 MPa (20 bar)
Max. temperature 70
oo
o
C
2
D
21
CCCCoooonnnnddddeeeennnnssssaaaattttiiiioooonn
Max. pressure 2 MPa (20 bar)
Temperature reduction: approx. 10
nn
C
o
C
Page 29
Legend
The component parts:
E
G
3
High pressure
Low pressure
A Compressor with magnetic clutch
B Low-pressure switch
C Condenser
D High pressure service connection
E Restrictor
F Evaporator
G Low-pressure switch
H Low-pressure service connection
I Collecting tank
4
F
In contrast to the circuit with expansion valve, the
liquid refrigerant is injected into the evaporator
through a restrictor.
In restrictor-regulated air conditioners, a
collecting tank is fitted at the low-pressure side in
place of the fluid container on the high-pressure
side.
This collecting tank serves as a reservoir and
protects the compressor (fluid shock). Also refer
to page 31.
208_007
All other components are identical to those used
in the circuit with expansion valve.
Additional connections for service work or
sensors for monitoring functions can be
integrated in the circuit, depending on circuit
design and necessity.
The pressures and temperatures are dependent
upon the momentary operating state of the
refrigerant circuit. The specified values are
achieved after a specific period depending on
the ambient temperature (refer to Workshop
Manual).
3
EEEExxxxppppaaaannnnssssiiiioooonn
from 2 MPa (20 bar) to > 0.15 MPa (1.5 bar)
Temperature: from 60
nn
o
C to > –4 oC
4
EEEEvvvvaaaappppoooorrrraaaattttiiiioooonn
Max. pressure > 0.15 MPa (1.5 bar)
Temperature: > –4
nn
o
C
1
208_033
29
Page 30
The cooling system
The restrictor
The restrictor is a narrowing in the refrigerant
circuit located directly upstream of the
evaporator. This narrowing “restricts“ the flow of
the refrigerant.
The refrigerant is warm under high pressure
upstream of the restrictor.
The pressure of the refrigerant drops rapidily
when it passes the restrictor.
The refrigerant is cold at low pressure.
The restrictor is therefore the “interface“ between
the high-pressure and low-pressure sides of the
refrigerant circuit. A seal ensures that the
refrigerant only passes the restrictor at the
narrowing.
208_035
Strainer for atomising the
refrigerant
Tasks
– To determine the flow rate of the refrigerant
by means of a calibrated bore. The amount of
refrigerant which can flow through this bore is
limited by the pressure in the refrigerant
circuit.
– To maintain the pressure on the high-pressure
side of the refrigerant circuit and keep the
refrigerant in a liquid state when the
compressor is running.
– The pressure in the restrictor drops. The
refrigerant cools down before it enters the
evaporator through partial evaporation.
– Atomisation of the refrigerant.
The restrictor has a dirt strainer upstream of the
narrowing.
A strainer for atomising the refrigerant before it
reaches the evaporator is located downstream
the narrowing.
To evaporator
Please note the installation position!
The arrow on the restrictor points to the
evaporator.
Calibrated bore
Dirt strainer
0-ring, seals the high-pressure
side off from the low-pressure
side
208_016
30
Page 31
The collecting tank
There is a collecting tank in the low-pressure part
of air conditioners with restrictor. This tank is
installed in a warm location in the engine
compartment (post-evaporation).
It serves as an equalising vessel and reservoir for
the refrigerant and refrigerant oil and also
protects the compressor.
The gaseous refrigerant coming from the
evaporator enters the tank. If there are traces of
moisture in the refrigerant, they are bound in the
integrated drier.
The refrigerant collects in the upper part of the
plastic cap and is certain to be in a gaseous state
when it is drawn in by the compressor through
the U-tube.
208_036
Intake point for gaseous refrigerant
As a result, the compressor draws in gaseous
refrigerant only, and no liquid droplets.
Protection of the compressor against damage is
thereby ensured.
The refrigerant collects at the base of the
collecting tank.
The refrigerant drawn in by the compressor
absorbs refrigerant through a hole in the U-tube.
A filter strainer prevents the ingress of impure
refrigerant through this hole.
The collecting tank must be kept closed
as long as possible prior to installation
(leave the sealing plugs on the
connections) in order to minimise
moisture absorption from the ambient
air in the drier.
From
evaporator
Filter strainer
Hole for refrigerant
Plastic cap
To
compressor
Drier
U-tube
208_037
31
Page 32
System control
1
2
p
t°
An air conditioner will only function if all system
components are working properly. Failure of one
of these components could cause the working
pressures to change. In this case, it is not possible
to rule out consequential damage to the system
and the engine. To avoid this, there are
monitoring devices in the refrigerant circuit.
10
3
9
7
8
4
5
The air conditioner does not necessarily
have to have all the components shown
in the diagram. Neither do these
components have to be connected in
this way.
The diagram shows the system control of a
simple manual air conditioner.
6
208_054
32
A control unit processes the signals from the
monitoring devices and controls the periodic
switch-off and switch-on of the compressor and
the speed of the fan. This ensures that the
pressure level in the refrigerant circuit always
adapts itself to the normal values.
In systems equipped with an open-loop
compressor, the signals from the monitoring
device are also used for adaptation to demand
for cooling.
(switch-on and switch-off the air conditioner in
accordance with demand for refrigeration.
Icing of the evaporator is avoided at the same
time.)
The diagram shows the basic layout of the air
conditioner.
1 Air conditioner switch
2 Pressure relief valve at compressor
3 Radiator fan
4 Air conditioner pressure switch
5 Coolant temperature sender
6 Radiator fan thermo switch
7 Evaporator temperature sender
8 Fresh air blower
9 Engine control unit
10 Magnetic clutch
Air conditioner control unit
(and/or radiator fan
control unit,
depending on system type)
Page 33
30
15
X
31
30
15
X
31
S
J
257
E
35
J
301
J
32
t1t
A
M
V
F
18
2
G
153
-t°
F
p
2
7
J
101
129
p
1
J
257
G
62
N
25
31
A Battery
E35 Air conditioner switch
F18 Radiator fan thermo switch
t
= 95 oC
1
t
= 103 oC
2
F129 Pressure switch for air conditioner
P
= 0.2 MPa (2 bar)/3.2 MPa (32 bar)
1
P
= 1.6 MPa (16 bar)
2
G62 Coolant temperature sender
G153 Evaporator temperature sender
J32 Air conditioner relay
J101 Radiator fan 2nd speed relay
J257 Mono-Motronic control unit
J301 Air conditioner control unit
N25 Air conditioner magnetic clutch
V7 Radiator fan
S Fuse
31
208_055
Simple functional example showing how the
compressor (via magnetic clutch N25) and radiator
fan are switched on and off.
Colour codes:
Positive
Negative
Input signal
Output signal
Bidirectional signal
t°
p
In the new-generation air conditioners,
there is a high pressure sender in place
of the pressure switch for air conditioner
(refer to page 36).
33
Page 34
System control
Components of the safety systems
Air conditioner switch E35
Pressure relief valve
p
t°
208_068
Switch for switching on the air conditioner – the
magnetic clutch makes the connection to the
compressor.
In automatically controlled systems, the radiator
fan and the fresh air blower start simultaneously.
In manual air conditioners, the fresh air blower
must be switched to the 1st speed.
A signal indicating that the air conditioner has
been switched on is transmitted to the engine
control unit, and engine idling speed is increased
(to compensate for load resulting from
compressor work).
The switch may be located downstream of an
ambient temperature switch.
This ensures that the air conditioner cannot start
when the temperature is below 5 °C.
The valve (previously: bursting seal) is attached
directly to the compressor or fluid container. The
valve opens at a pressure of approx. 3.8 MPa
(38 bar) and closes when the pressure drops
(approx. 3.0 - 3.5 MPa/30 - 35 bar).
Depending on type, a plastic disc which ruptures
as soon as the valve lifts can be attached.
In this case, the cause of the excess pressure in
the system must be determined.
The bursting seal should only be replaced when
the system is empty.
34
Evaporator temperature sender G153
208_056
208_061
The evaporator temperature sender measures
the temperature between the cooling fins of the
evaporator. The sender signal is transmitted to
the air conditioner control unit. When the
evaporator temperature drops too low, the
compressor is switched off.
The compressor is switched off at approx. –1 °C
to 0 °C and switched on at approx. +3 °C
Icing of the evaporator by freezing condensation
water is prevented.
In some systems, evaporator temperature switch
E33 is used in place of this sender. The power
supply to the magnetic clutch is opened directly
by means of this switch.
Other systems control this function by means of
an ambient temperature switch.
Page 35
Pressure switch F129
208_057
To monitor and/or limit the pressure conditions in
the closed refrigerant circuit, high-pressure and
low-pressure switches are installed on the high
pressure side.
If unacceptable pressures build up inside the
system, the compressor will be switched off via
the magnetic clutch.
The pressure switch can be directly integrated in
the line or attached to the fluid container.
Pressure switch F129 is a 3-way combination
switch for:
– safeguarding the cooling air flow (fan circuit)
– safeguarding the pressure conditions.
The pressure switch operates in the following
conditions:
p > 3,2 MPa =
p < 0,2 MPa =
p > 1,6 MPa =
208_058
208_059
208_060
– it switches off the magnetic clutch via the air
conditioner control unit at an excess pressure
of approx. 2.4 to 3.2 MPa (24 to 32 bar). This
excess pressure can be caused by a dirty
condenser, for example.
– it switches off the magnetic clutch via the air
conditioner control unit when the pressure
drops below a minimum value (0.2 MPa/
2bar) . This can be caused by loss of
refrigerant, for example.
– it switches the fan one speed higher at 1.6
MPa (16 bar) excess pressure. As a result,
condenser performance is optimised.
t°
p
35
Page 36
System control
t°
p
High pressure sender G65
Signal utilisation
in the engine control unit
in the radiator fan control unit
208_062
– A new generation of senders for monitoring
the refrigerant circuit.
– Air conditioner pressure switch F129 has been
replaced by an electronic pressure sensor.
The evaluation electronics in the air conditioner and engine control units have been adapted accordingly.
– Like pressure switch F129, the high pressure
sender is integrated in the high pressure line.
It registers the refrigerant pressure and converts
the physical quantity of pressure to an electrical
signal.
Unlike the air conditioner pressure switch, the
sender registers not only the defined pressure
thresholds, it also monitors the refrigerant
pressure throughout the working cycle.
These signals indicate the load being exerted on
the engine by the air conditioner and the
pressure conditions in the refrigerant circuit. The
next higher stage of the cooling fan and the
magnetic clutch of the compressor are activated
and deactivated via the radiator fan control unit.
Substitute function
Advantages
Self-diagnosis “fault message“
If the radiator fan control unit fails to detect any
signals, then the compressor will be switched off
for safety reasons.
– The idling speed of the engine can be
adapted exactly to the power consumption of
a specific compressor.
– The radiator fan speed activation and
deactivation cycles are staggered with a short
time delay.
As a result, changes in the speed of the
cooling fan are barely perceptible at idling
speed. This enhances comfort especially in
vehicles with engines with low power outputs.
The fault in the high pressure sender is stored to
the fault memory of the eeeennnnggggiiiinnnneeee eeeelllleeeeccccttttrrrroooonnnniiiiccccssss .
e.g.: 00819 high pressure sender G65
“Signal too low“
36
Page 37
Function of high pressure sender
2V/Div 5ms/D
A
B
At low pressure
0
208_109
Pulse-width
modulated
signal
Microprocessor
The refrigerant pressure is applied to a silicon
crystal. Depending on the pressure level, the
crystal will be more or less “deformed“.
The silicon crystal, together with a
microprocessor, is integrated in the sensor and
supplied with voltage.
One of the properties of the silicon crystal is that
its electrical resistance changes when it is
deformed. Depending on the pressure
characteristic, a test voltage picked off at the
silicon crystal also changes as a result.
The test voltage is conducted to the
microprocessor and converted to a pulse-width
modulated signal (A = pulse width, B = signal
distance).
At a low pressure, the crystal undergoes minimal
“deformation".
The voltage applied is therefore only opposed to
a low electrical resistance.
The voltage change is small.
t°
p
208_063
Pulse width signal
Period duration 20 ms
Pulse width 2.6 ms
Voltage
Test voltage
Silicon crystal
(resistance)
The microprocessor of the high pressure sender
outputs a small pulse width at low pressures.
Pulse width signals are generated at a frequency
of 50 Hz per second.
This is equivalent to a period duration
of 20 ms = 100%.
At a low pressure of 0.14 MPa (1.4 bar), the pulse
width is 2.6 ms.
This is equivalent to 13% of the period duration.
208_064
37
Page 38
System control
At high (increasing) pressure At high (increasing) pressure, the crystal is
“deformed“ more, so the change of resistance is
larger. The test voltage decreases
proportionately.
Pulse-width
modulated
signal
Microprocessor
Voltage
Test voltage
Silicon crystal
(resistor)
208_065
p
t°
Pulse width signal The pulse width increases in proportion to the
Period duration 20 ms
increasing pressure.
At a high pressure of 3.7 MPa (37 bar), the pulse
width is 18 ms. This is equivalent to 90% of the
period duration.
Pulse width 18 ms
208_066
Using the digital memory oscilloscope
of the new vehicle diagnosis system
VAS 5051, it is possible to visualise the
pulse width signal.
38
Page 39
Disconnected safety switch in the
refrigerant circuit with restrictor
F73
F118
208_067
In the refrigerant circuit with restrictor, the low
pressure and the high pressure are often
monitored by two separate safety switches.
Low pressure
Air conditioner low-pressure switch F73 switches
off the compressor when the pressure drops
below approx. 0.17 MPa (1.7 bar) in the
refrigerant circuit, for example.
(This pressure drop can occur if the refrigerant
level in the circuit is too low.
The compressor is protected.)
High pressure
Magnetic clutch high-pressure switch F118
switches off the compressor when the pressure
exceeds approx. 3.0 MPa (30 bar) for example.
The absolute values should always be regarded
as being system-specific.
Coolant temperature switch with pilot lamp
In vehicles with extended electronic
sensor evaluation via the
control unit combination of the vehicle,
this additional check is no longer
necessary. The signal generated by the
primary monitoring device is utilized.
208_069
The compressor constitutes an additional load
for the engine.
To avoid overheating the coolant when the
engine is under heavy load, e.g. when travelling
uphill, the additional compressor load is
switched off.
For this purpose, the coolant temperature is
monitored additionally by a coolant temperature
switch with a pilot lamp.
(The primary monitoring device is the coolant
temperature sender with indicator lamp in the
dash panel insert.)
The compressor cuts out at approx. 119 °C and
cuts in at approx. 112 °C.
Various switches with pilot lamp are used
depending on vehicle type, e.g.
F18 - Radiator fan thermo switch
F163 - Air conditioner
cut-off thermo switch.
t°
p
39
Page 40
Cooling fan circuit
Circuit connecting fan to engine/
condenser cooling system
shown using the VW Golf/Audi A3 as an
example
Fan operation is a basic condition for proper
functioning of an air conditioner (refrigerant circuit)
and the engine (coolant circuit). Condenser
performance will be impaired if there is no cooling.
Proper functioning of the air conditioner is no
longer assured. In air conditioning, a second or
third fan is often also used.
Cooling fan 2nd auxiliary fan
Thermo switch F18
1st auxiliary fan
Radiator fan control unit J293
These fans provide the necessary fresh air flow
through the radiator and condenser.
The fan control regulates radiator fan control unit
J293
depending on the temperature of the coolant and
the pressure in the refrigerant circuit.
The absolute values are always vehicle-specific!
Air conditioner pressure
switch F129
CCCCoooooooollllaaaannnntttt tttteeeemmmmppppeeeerrrraaaattttuuuurrrree
The signal generator is radiator
fan thermo switch F18.
The thermo switch is located in the vehicle
radiator.
Speed 1 ON 92 .. 97
Speed 2 ON 99 .. 105
PPPPrrrreeeessssssssuuuurrrreeee iiiinnnn rrrreeeeffffrrrriiiiggggeeeerrrraaaannnntttt cccciiiirrrrccccuuuuiiiitt
The signal generator is
air conditioner pressure switch F129 or the high
pressure sender G65.
F129 switches the fan(s) to speed 2at a pressure
of approx. 1.6 MPa (16 bar) (also refer to
page 35).
Example: Check functions
ee
OFF 84 .. 91
OFF 91 .. 98
tt
Example: 2-fan combination
– The air conditioner is switched on, therefore
the compressor is switched on and the
pressure in the refrigerant circuit is greater
than 0.2 MPa (2 bar).
= both fans run at speed 1
o
C
o
C
o
C
o
C
– High pressure in the refrigerant circuit is
greater than 1.6 MPa (16 bar) and/or coolant
temperature is above 99
= both fans run at speed 2
– If the pressure in the refrigerant circuit drops
below 1.6 MPa (16 bar) and the coolant
temperature is below 99
= both fans will again run at speed 1
– When the engine is being operated without
the air conditioner, only the cooling fan will be
running. The fan will be running at speed 1 or
2 depending on coolant temperature.
o
C
o
C
40
Page 41
Radiator fan control unit J293
208_070
The radiator fan control unit is integrated in the
vehicle control system.
Incoming signals in the basic version:
– from thermo switch F18
– from pressure switch F129
– from operating and display unit E87 (with
automatic air conditioner)
Tasks
To convert the incoming signals
– To switch the cooling fan on and off
– To switch the compressor magnetic clutch on
and off.
Expanded functions of a new generation:
Radiator fan control unit J293 has been
developed technically and adapted functionally
to the new high pressure sender G65.
New generation
There are also circuit variants where the
functions of the control units are
assumed by an air conditioner control
unit.
Integration in their control system is
always vehicle-specific.
For details, please refer to the current
flow diagram.
It is fitted together with the high pressure sender
and, as a distinguishing feature, has modified
plug connections.
The control unit evaluates the pulse-width
modulated signal from the high pressure sender.
The overall pressure range of the refrigerant
pressure is monitored continously in this way.
Functions
– To switch the radiator fan speeds and the
magnetic clutch of the air conditioner compressor on and off
– Bidirectional signal interchange with the
engine and gearbox control unit
– Monitoring the coolant temperature
– with timer module for activating coolant run-
on pump V51 (e.g. 1.8-ltr. 5 V engine 165 kW)
41
Page 42
Temperature control
Manual control
Fresh air blower
Refrigerant circuit
Evaporator
Fresh-air flow
Temperatureadjusted
interior air
Condenser
Why temperature control?
– The fresh-air flow cooled down at the
evaporator is pumped into the passenger
cabin by means of the fresh air blower.
– This air is usually cooler than necessary
(blower capacity is designed for maximum
cooling, however the prevailing ambient
temperatures are usually moderate).
– To attain a pleasant interior temperature, a
portion of the cold fresh air flow is therefore
ducted over the heat exchanger the heating
system and heated up.
– Temperature fluctuations can also be caused
by different ambient temperatures, road
speeds, coolant temperatures, fresh air
supplies etc.
– In the case of simple manual air conditioners,
the driver has to regulate the temperature.
Heat exchanger
What is regulated?
– Registration of actual values, i.e. temperature
sensing.
– Setpoint/actual value comparison, i.e. the
driver performs an individual evaluation. The
driver defines the comfort temperature, i.e.
whether too warm or too cold.
– Based on the evaluation, the driver decides
whether
• the temperature needs to be adjusted
• in what direction
• by how much
and makes this adjustment manually.
The driver is, in the figurative sense, both the
controller and the actuator.
The driver adjusts the temperature flap.
208_075
42
Page 43
Automatic control
Fresh air intake duct
temperature sensor
Sunlight penetration
sender
Dash panel temperature
sensor
Control unit
Ambient temperature
sensor
Automatic air conditioners relieve the driver of
this task.
They have the advantage that they can include
many more parameters in the control system and
calculate the thermal result of your adjustment in
advance.
Various names are used to describe electronic
air conditioner controls:
– Digital temperature control
– Climatronic
– Air conditioner with automatic control
What they all have in common is:
– a control unit
– ambient temperature sensor (one or two)
– interior temperature sensor
– additional senders (not in every system), e.g.
sunlight penetration sender
– Positioning motors on the heater/air conditio-
ner
Footwell vent
temperature sender
208_076
The diagram shows the positions of the sensors.
The digital control unit is the master station.
It processes all input signals from the sensors
(information sender), interference-suppresses
them and feeds them to the microcomputer in the
control unit.
The microcomputer calculates the output signals
in accordance with the pre-programmed
setpoints.
The output signals are fed to the actuators via
output stages.
The actuators are the positioning motors on the
heater/air conditioner.
Suitable positioning motors are assigned to the
flaps.
Air conditioners of the current generation are
linked to other vehicle control units either directly
or via the CAN-BUS. Information on road speed,
on engine speed and on ´time parked´ are also
included in the evaluation of the air conditioner
control unit in this way.
43
Page 44
Temperature control
T
System overview of an electronically controlled air conditioner
(the temperature is regulated evenly at the left- and right-hand sides of the passenger cabin as shown
using the Golf as an example. An identical system is used in the Audi A3)
Sensors
(for system control and temperature
control)
Sunlight penetration
photo sensor G107
Temperature sensor
Dash panel
Temperature sensor G56
Blower V42
Ambient temperature
sensor G17
CLIMAtronic
AUTO
ECON
CLIMA
Temperature sensor
Fresh air intake duct temperature
sensor G89
Footwell vent
temperature sender
G192
Air conditioner
pressure switch F129
Auxiliary signals:
- road speed signal
- engine speed signal
- 'time parked' signal
Coolant temperature warning switch
(overheating) F14
v
n
t
h
44
Radiator fan
thermo switch F18
Page 45
Climatronic control unit J255
and Air conditioner/Climatronic
operating and display unit E87
Actuators
(for system control and
temperature control)
Footwell/defroster flap
positioning motor V85
with potentiometer G114
Central flap
positioning motor V70
with potentiometer G112
MATRONIC
AUTO
ECON
Temperature flap
positioning motor V68
with potentiometer G92
Air flow flap
positioning motor V71 and air
recirculation flap
with potentiometer G113
Fresh air blower
Control unit J126
and fresh air blower V2
Auxiliary signals:
- engine control unit
- control unit with display
unit in dash panel
insert
Diagnosis plug connection
T16
Radiator fan control unit
J293
208_077
Magnetic clutch
N25
Radiator fan, right V7 and
auxiliary fan V35
45
Page 46
Temperature control
Control unit with operating and
display unit
Dash panel temperature
sensor G56
Climatronic control unit with
operating and display unit
Design
CLIMATRONIC
Control unit
AUTO
ECON
Operating and
display unit E87
ECON
OTUA
Dash panel temperature
sensor G56
Control unit with operating and
display unit of Audi TT Coupé
OFF
208_078
208_101208_102
The control unit is combined with the operating
and display unit which is adapted to the design
of the vehicle in question.
A vehicle interior temperature sensor is also
integrated in the control unit.
Function
The control unit receives information from the
electrical and electronic components (sensors).
These signals are processed by the control unit in
accordance with the setpoints. The output signals
of the control unit then control the electrical
actuators.
The control unit is equipped with a fault memory.
Failure of a component or an open circuit can be
detected quickly via the self-diagnosis.
No matter what fault occurs, the control unit will
remain in operation and maintain the
temperature settings in emergency mode.
46
Page 47
Actuators/sensors on a heater/
air conditioner
Footwell/defroster flap
positioning motor
Fresh air intake duct
temperature sensor
Air flow flap positioning
motor and air recirculation
flap
Fresh air blower
Fresh air blower
control unit
Footwell vent
temperature sender
Temperature flap
positioning motor
(concealed)
A positioning motor is assigned to each flap for
air ducting in the heater/air conditioner.
The air flow flap and air recirculation flap are
driven by a positioning motor. These flaps are
adjusted separately by a driving pulley with two
guide rails.
In other systems, the air recirculation flap can
also be adjusted by means of vacuum and
solenoid valves.
Central flap
208_079
positioning motor
In this case, the fresh air blower and fresh air
blower control unit are separate components.
However, they can also be combined to a unit.
47
Page 48
Temperature control
The main temperature sensors
Ambient temperature sensor G17
The temperature sensor is positioned in the
vehicle front section.
It registers the actual ambient temperature.
Signal utilisation
The control unit controls the temperature flap
and the fresh air blower in dependence upon the
temperature.
Effects of signal failure
If the signal fails, the measured value of the
second temperature sensor (temperature sensor
in fresh air intake duct) is utilised.
If this signal also fails, the system continues to
operate by assuming a substitute value of
o
+10
C. Air recirculation is not possible.
The temperature sensor has self-diagnostic
capability.
208_081
Fresh air intake duct
temperature sensor G89
The temperature sensor is located directly inside
the fresh air intake duct.
It is the second actual ambient temperature
measuring point.
Signal utilisation
The control unit controls the temperature flap
and the fresh air blower in dependence upon the
temperature.
Effects of signal failure
If the signal fails, the measured value of the first
temperature sensor (ambient temperature
sensor) located in the vehicle front section is
utilised. The temperature sensor has selfdiagnostic capability.
Both temperature sensors always
process the lowest value.
208_082
48
Page 49
Dash panel temperature sensor G56 with
temperature sensor blower V42
The temperature sensor is usually integrated
directly in the control unit and transfers the
actual interior temperature to the control unit.
It is located in the air stream of a fresh air blower
which is used to draw off interior air.
The fresh air blower is activated by the operating
and display unit.
It draws off the interior air in order to avoid
measurement errors at the temperature sensor.
Signal utilisation
The measured value is used for comparison with
the setpoint.
The temperature flap and the fresh air blower
are controlled accordingly.
Effects of signal failure
In the event of signal failure, a substitute value of
o
+24
C is assumed. The system remains in
operation.
The temperature sensor has self-diagnostic
capability.
Fresh air blower
Temperature
sensor
CLIMATRONIC
AUTO
ECON
208_083
Footwell vent
temperature sender G192
The temperature of the air flowing out of the
heater/air conditioner (and into the vehicle
interior) is measured. The temperature is
registered with a temperature-dependent
resistance.
The electrical resistance increases as the
temperature drops.
Signal utilisation
The signal is evaluated by the control unit. The
signal is used to control the defrost/footwell air
distribution and the volumetric capacity of the
fresh air blower.
Effects of signal failure
In the event of signal failure, the control unit
calculates a substitute value of +80
o
C.
The system remains in operation.
The sender has self-diagnostic capability.
208_084
49
Page 50
Temperature control
Sunlight penetration photo sensor G107
Air conditioner temperature is controlled by
means of photo sensors.
They register the direct sunlight exposure of the
vehicle occupants.
Depending on air conditioner type, they can
measure sunlight penetration via one or two
sensors and separately for the left- and righthand sides of the vehicle.
Function
The sunlight passes through a filter and an
impinges upon an optical element on the photo
diode. The filter functions in much the same way
as sunglasses and protects the optical element
against UV radiation.
Photo diodes are light-sensitive semiconductor
elements. When there is no incident light, only a
small current can flow through the diode. This
current increases when the photo diode is
exposed to sunlight. The stronger the incident
sunlight, the higher the current.
When the current increases, the air conditioner
control unit recognises that the sunlight is
stronger and regulates the interior temperature
accordingly. The temperature flap and fresh air
blower are controlled accordingly.
In the version with two sensors, the side of the
vehicle exposed to stronger sunlight is cooled
more (refer to page 58).
Effects of signal failure
The control unit utilises an assumed fixed value
for sunlight penetration.
192_093
Housing
cover
Filter
Optical
element
Photo diode
Housing,
192_034
A B
50
Electrical circuit
Air conditioner control unit
G107 Photo sensor
A 1 sensor
B 2 sensors
G107 G107
208_088
Page 51
Auxiliary signals for temperature control
4
3
1/min x 1000
2
1
5
6
7
Combination processor in
dash panel insert
t
h
Air conditioner
control unit
To temperature
flap
Heater/air
conditioner
With regard to temperature control, additional
information enhances comfort and is utilised for
system control.
These auxiliary signals are supplied by other
vehicle control units and are processed by the air
conditioner control unit.
Important signals are:
– ’Time parked ’t
h
– Road speed v
– Engine speed n
'Time parked' signal th
120
100
140
km/h
80
60
40
20
n v
160
180
200
220
240
n
To air flow flap
Changes in measured data (e.g. due to radiant
heat) are disregarded for control purposes.
The comfort temperature is set quickly and
exposure to subnormal temperatures is avoided.
Road speed signal v
Is required to control the air flow flap.
The signal generated by the speedometer sender
is utilised and implemented in the control unit. At
higher road speeds, the cross-section of the fresh
air inlet is reduced in order to keep the air flow
into the passenger cabin as steady as possible.
Engine control unit
Radiator
control unit
Compressor
208_087
Time parked=the time between switching off the
ignition and restarting the engine
This signal is utilised for adjusting the
temperature flap. When the engine is restarted,
the control unit processes the ambient
temperature values stored before turning off the
engine.
Engine speed signal n
This signal provides information to the air
conditioner control unit on actual engine
operation. It is required for system control (to
switch off the magnetic clutch), e.g. if there is no
engine speed signal, the compressor is switched
off.
51
Page 52
Temperature control
Positioning motor
In a manual air conditioner, air-ducting flaps
such as
– the temperature flap
– the central flap
– the footwell/defrost flap
are adjusted individually by the driver by means
of Bowden cables.
In the automatically controlled air conditioner,
the flaps are operated by electrically activated
positioning motors. The air recirculation flap is
also positioning motor operated.
The positioning motors are always positioned
level with the flap axis on the heater/air
conditioner .
All motors receive the corresponding control
signals from the air conditioner control unit.
Each positioning motor has a potentiometer. The
potentiometer signals the position of the flap to
the control unit in the form of a feedback value.
Thus, the electrical output signals are converted
to mechanical quantities by means of positioning
motors (actuators).
208_115
1 positioning motor
each for
- temperature flap
- central flap
- footwell/defrost
Electrical circuit
208_091
208_116
Positioning motor for fresh air
recirculation flap and air flow flap
Air conditioner
control unit
52
The flaps have different adjustment
mechanisms.
The arrangement of the cranks and
angle of rotation are always referred to
a particular flap.
Sender
information
+
5V
-
M
Positioning
motor with
potentiometer
208_092
Page 53
Air ducting
The heater/air conditioner
Defrost
Footwell
outlet
Dash panel
outlet
Fresh air
Air flow flap
Fresh air/air
recirculation
flap
Fresh air blower
Fresh air
208_093
Heat exchanger
Defrost
Footwell
outlet
Dash panel
outlet
Air conditioning mode
Air flow flap
Fresh air/
air recirculation
flap
Fresh air blower
Evaporator
208_112
Air ducting in the heater/air conditioner
Undivided air ducting – diagram –
for maximum refrigeration output
Very warm fresh air is ducted to the air outlet
via the evaporator. The channel to the heat
exchanger is closed.
Air ducting and distribution are always
dependent upon the design of the heater/air
conditioner and by the required level of driving
comfort.
A basic distinction is made between
– undivided air inflow into the passenger cabin
– divided air inflow for the left- and right-hand
sides of the passenger cabin.
The latter version, of course, requires more
sensors, actuators and air flaps.
53
Page 54
Temperature control
Heat exchanger
Fresh air
Temperature flap
Air ducting in the heater/air conditioner
Undivided air ducting – diagram–
for maximum heat output
All heaters/air conditioners are basically
designed as shown in the diagram:
Air conditioner OFF,
heating ON
Evaporator
208_110
Very cool fresh air flows through the evaporator;
evaporator is not working.
Fresh air is passed over the heat exchanger and
heated.
– Air inlet for ambient air
– Air inlet for air recirculation mode (if provi-
ded)
– Fresh air blower
– Evaporator (for cooling the air down)
– Heat exchanger (for heating the air up)
– Regulating flaps and ducts for selective air
ducting (footwell, defrost, dash panel outlet).
54
Page 55
Fresh air
Air ducting in the heater/air conditioner
Undivided air ducting – diagram–
for mixed operation
Air conditioner ON,
heating ON
= individual
adjustment range
208_114
208_111
Warm fresh air flows through the evaporator in order to
cool down. The fresh air is too cool, therefore a partial
air flow is ducted over the heat exchanger in order to
attain the individually selected vent temperature.
Air conditioning mode can be selected
even if the fresh air is cool and moist.
The fresh air passing over the
evaporator is dehumidified and the
windows are demisted.
55
Page 56
Temperature control
Different ambient temperatures
Constant interior temperature
208_094
Automatic flap control and
through
switching the air conditioner on and off
208_095
208_096
208_098 208_099
208_097
56
Page 57
Air distribution –
split into two separate air flows in the
automatic system
(example: Audi A6)
In this case, air distribution inside the vehicle is
regulated by air-side flaps in the air conditioner
(in the Audi A8, air distribution is regulated on
the water side).
Depending on flap control, the air flow is ducted
to the individual air outlets.
All flaps are actuated electrically by the
positioning motors.
The flaps are adjusted either automatically
according to program flow, or manually at the
operating and display unit.
Air distributor housing
Evaporator
Temperature
flaps
Passenger cabin, rightPassenger cabin, left
194_099
Heat exchanger
208_100
The temperature flaps
In this version, the temperature for the left- and
right-hand sides of the passenger cabin can be
adjusted independently.
In the air distributor housing, the air flow is
divided into cold/warm and passenger cabin
left/right.
Depending on temperature requirements, the
proportion of warm and cold air for the
passenger cabin can be adjusted with the
temperature flaps.
The temperature flaps are actuated by
– a positioning motor for the left-hand side of
the passenger cabin
– a positioning motor for the right-hand side of
the passenger cabin.
57
Page 58
Temperature control
System overview a electronic regulated air conditioner
(with separate air-side temperature control for the left- and right-hand sides of
the passenger cabin, as shown using the Audi A6 as an example)
Sensors
Sunlight penetration
photo sensors G107
Dash panel
temperature sensor G56
with temperature sensor
blower V42
Ambient temperature
sensor G17
Temperature sensor
Fresh air intake duct G89
Vent temperature sender, right
G151
Vent temperature sender, left
G150
Footwell vent temperature sender
G192
58
Air conditioner pressure switch F129
Auxiliary signals
Page 59
The temperature can be set differetly for the leftand right-hand sides to between 18
o
29
C.
Control unit J255 or
air conditioner operating and
display unit E87
o
C and
The temperature flaps for left/right temperature
distribution are located in the air distributor
housing
Actuators
Air flow flap positioning motor
and fresh air/air recirculation flap
V71
with potentiometer G113
Defrost flap positioning motor
V107
with potentiometer G135
Left temperature flap
positioning motor V158
with potentiometer G220
Right temperature flap positioning
motor V159
with potentiometer G221
Central flap and footwell flap
positioning motor V70
with potentiometer G112
Fresh air blower V2 and
fresh air blower control unit J126
Diagnostic connection
194_072
Magnetic clutch N25
Auxiliary signals
59
Page 60
Temperature control
Air recirculation mode
What do we mean by air recirculation mode?
The air conditioner processes two types of air,
namely ambient air and cabin air (air
recirculation).
In air recirculation mode, the air used for cooling
the passenger compartment is not extracted from
the outer atmosphere, rather from the vehicle
interior.
Therefore, the system only recirculates and
controls the temperature of the air which is
available inside the vehicle.
Why air recirculation mode?
30
Air recirculation mode
20
[
C
10
[
T
0
-10-10
2 4 6 8 10 12 14 16
0
Fresh air mode
]
t
[
min
208_089
Air recirculation mode is the quickest way to cool
down the vehicle interior. This is done by
recycling the cabin air, which is always cooler.
When heating the vehicle interior, the converse
effect occurs, i.e. the air is heated more rapidly.
An advantage of air recirculation is that the
evaporator output or compressor drive output
required is more than halved in air recirculation
mode.
In addition to rapid cooling/heating, air
recirculation mode can be used to avoid
breathing in polluted ambient air (unpleasant
odours, pollen).
Does air recirculation mode have any drawbacks?
In air recirculation mode, there is no air
exchange. The air will be “used up“.
Therefore, air recirculation mode should not be
used any longer than is necessary, and for no
more than 15 minutes.
In air recirculation mode, the atmospheric
humidity in the passenger cabin rises due to
moisture released with the air respired by the
occupants. When the dew point of the interior air
exceeds the temperature of the windows, the
windows will inevitably mist up.
Average values for vehicle temperature reduction/
increase in the air recirculation and fresh air modes
Fresh air flap
Vacuum box
Cabin air
Air recirculation flap
208_117
60
In the Defrost setting, therefore, air
recirculation mode is automatically
disabled.
Vehicle air conditioning
in air recirculation mode – pneumatically operated
Page 61
Manual air recirculation mode
With the manual air conditioner, the driver is
responsible for controlling and operating air
recirculation mode.
The driver decides on when and for how long.
After pressing the air recirculation button, the
flaps are adjusted pneumatically with vacuum.
With automatic air conditioners, too, air
recirculation mode is mainly selected manually
by the driver.
In this case, the fresh air/air recirculation flap is
adjusted electrically by means of a positioning
motor.
What both systems have in common is
– Fresh air flap closed
= air recirculation flap open
– Fresh air flap open
= air recirculation flap closed
The air recirculation flap positioning motor is
also used to adjust the air flow flap.
Air recirculation button – manual air
conditioner
OFF
Air recirculation button – automatic air
conditioner
Positioning motor
Air flow flap
ECON
AUTO
208_118
207_043
Several versions of automatic air conditioners
already control air recirculation mode
automatically.
As soon as pollutants enter the ambient air, the
fresh air supply is blocked.
These systems have additional system
components.
Fresh air
recirculation flap
Cabin air
208_090
Vehicle air conditioning
in air recirculation mode – electrically operated
61
Page 62
Temperature control
AAAAuuuuttttoooommmmaaaattttiiiiccccaaaallllllllyyyy ccccoooonnnnttttrrrroooolllllllleeeedddd aaaaiiiirrrr rrrreeeecccciiiirrrrccccuuuullllaaaa--
CS
2
ee
H S
2
C H
6 14
ttttiiiioooonnnn mmmmooooddddee
Airborne pollutants
In systems with a manually operated air
recirculation mode, the changeover is logically
not performed by the driver until an odour
nuisance occurs, by which time the air inside the
vehicle will have already been fouled.
In systems with an automatic air recirculation
mode, the vehicle ventilation system will be
closed as soon as pollutants in the air have been
detected (by a sensor), i.e. before an odour
nuisance occurs. The automatic air recirculation
function can be switched on and off manually.
The system components
NO
SO
CO
C H
6 6
x
2
Fresh air
intake
--
Combination filter
Operating and display unit with automatically
controlled air recirculation mode
Air quality
sensor G238
+
-
Manual function switch on/off
button
Signal to
operating and
display unit E87
208_105
208_108
– Air quality sensor G238
An electronic component which is located in
the area of the fresh air intake upstream of
the combination filter.
– Combination filter
The combination filter replaces the dust and
pollen filter. It comprises a particle filter containing activated charcoal.
The operating principle
A gas sensor detects pollutants in the ambient
air. When a high pollutant concentration occurs,
the air conditioner control unit implements the
signal which the gas sensor generates by
changing over from fresh air mode to
recirculation mode.
If the pollutant concentration drops below a
given threshold, then fresh air is again supplied
to the vehicle interior.
What pollutants are detected?
The primary pollutants contained in the exhaust
gases of the petrol engine are:
CO - Carbon monoxide
C
- Hexane
6H14
C
- Benzene
6H6
C
- n-heptane
7H16
In exhaust gases of diesel engines:
NO
- Nitrogen oxides
X
- Sulphur dioxide
SO
2
H
S - Hydrogen sulphide
2
CS
- Carbon bisulphide
2
62
Page 63
Air quality sensor G238
The sensor operates, in principle, in much the
same way as a lambda probe.
The metering element is a mixed oxide sensor
which uses semiconductor technology (stannic
oxide - SnO
).
2
The sensitivity of the air quality sensor is
increased by catalytic additives of platinum and
palladium.
The operating temperature of the sensor is
approx. 350
o
C. Its power consumption of
0.5 watts is very low.
Air quality sensor G238
+
-
208_106
The evaluation electronics in the sensor
The evaluation electronics integrated in the
ultrasonic sensor module react to changes in
sensor conductivity.
High sensitivities are achieved.
The system is self-learning.
The electronics determine the average pollutant
concentration in the ambient air and sends
information on the type and quantity of the
materials by means of a digital square-wave
signal to the air conditioner control unit.
The control unit now closes the air recirculation
flap at peak pollution levels depending on the
ambient temperature and air pollution level.
This ensures that the ventilation system does not
remain stuck in air recirculation mode in heavily
polluted areas.
Regardless of the electronic evaluation, several
systems switch to air recirculation mode when the
wash/wipe system is operated.
Service
The air quality sensor is wear-free.
The combination filter must be replaced after
service intervals.
Ambient
temperature
o
> +2
C Low
o
> +2
C Low no
o
C ... –5 oC Higher
+2
o
< –5
C Higher
ECON mode
compressor off
Defrost mode no
Warm-up phase of sensor
approx. 30 sec.
Air pollution
G238
M
level
rise
rise
rise
E87
Air quality
sensor
Digital
square-wave
signal
Air conditioner
control unit
Positioning motor for
air recirculation
mode
208_107
Air recircula-
tion
yes
min. 25 sec.
yes
max.
15 sec.
max.
15 sec.
no
63
Page 64
Technical Service
Safety precautions for working on
air-conditioned vehicles and handling refrigerant R134a
Set codes of conduct and safety precautions
must be observed when working on airconditioned vehicles and handling refrigerants in
order to ensure that no-one is endangered by
leaking refrigerant.
Work performed incorrectly can also damage
the air conditioner itself and should therefore be
avoided at all costs in the interests of proper
customer care.
Wear protective gloves
General servicing work on the vehicle should
be prepared
and performed in such a way that the vehicle
refrigerant circuit is not opened (e.g. radiator/
engine removal).
Direct contact with refrigerant should be avoided at all costs in order to avoid skin damage
(frostbite).
Escaping refrigerant has a temperature of –
o
26
C.
If it is necessary to open the refrigerant circuit
in order to perform repair work on the vehicle,
bring the vehicle to a service station for air
conditioners. At the service station, the refrigerant circuit will be emptied by expert personnel.
Important!
Wear protective
goggles
What is the correct code of conduct
when refrigerant discharged accidentally from
the refrigerant circuit comes into contact with
the skin?
If liquid refrigerant comes into contact with the
eyes, rinse eyes thoroughly with water for
15 minutes.
Then apply eye drops and contact a doctor even
if no eye irritation has occurred.
Inform the doctor that refrigerant was the cause.
In the event of skin contact, remove wet clothing
immediately and rinse the areas of skin affected
with copious amounts of water.
Naked flames, exposure to direct
sunlight and smoking are prohibited.
208_085
64
These are the only workshops which have the
equipment required to draw off refrigerant
properly. The refrigerant will also be processed
in an environmentally friendly manner and can
be reused.
Page 65
Neither welding or brazing or soldering work
may be performed on parts of the filled air
conditioner.
This also applies to welding and brazing/
soldering work on the vehicle if there is a danger
of parts of the air conditioner heating up.
During spot painting work, the object
temperatures in the drying oven or preheating
zone may not exceed 80
Why not?
Heating produces a higher excess pressure in the
system which can cause the pressure relief valve
to open. During electrical welding work, invisible
ultraviolet rays can penetrate the refrigerant
hoses and degrade the refrigerant.
o
C.
208_119
What is the correct code of conduct?
Damaged or leaky parts of the air conditioner
may not be repaired by welding or brazing/
soldering them. Such parts must always be
renewed. Draw refrigerant out of the refrigerant
circuit with the service station beforehand.
Work may only be performed on the
refrigerant circuit in well-ventilated rooms.
Refrigerant may not be stored in shafts or at
basement windows.
Why not?
Refrigerant is a colourless and odourless
substance. It is also heavier than air, and
therefore displaces oxygen and can flow down
into lower regions. If refrigerant escapes even
though all the applicable safety precautions
have been observed, there is an unforeseeable
risk of suffocation in badly ventilated rooms or
assembly pits.
Although refrigerant is not highly flammable, it is
not permitted to smoke or performe welding or
soldering or brazing work in a room filled with
refrigerant.
Why?
The high temperature of an open flame or a hot
object will cause chemical fission of the
refrigerant gas. Inhalation of the resulting toxic
fission products will lead to dry coughing and
nausea.
What is the proper code of conduct?
If a person breathes in refrigerant vapours in a
high concentration, bring the victim out into the
open air immediately.
Contact a doctor.
If the victim is having difficulty breathing,
provide the victim with oxygen.
If the victim has impaired breathing or is no
longer breathing, bend the victim's head back
and administer artificial respiration.
65
Page 66
Technical Service
Why service station for air
conditioners
and
special equipment?
The refrigerant circuit is in a closed system.
To ensure that the system functions properly:
– the refrigerant must be clean
– the refrigerant may not contain any moisture
– the piping must be evacuated and dry before
being filled
– only refrigerant resistant original spare parts
may be used.
To avoid damaging the environment and
physical injury,
– the refrigerant circuit may not be filled in the
open air
– the refrigerant must be disposed of in an
environmentally friendly manner.
What equipment does the service station
for air conditioners have for carrying out
work expertly and in an environmentally
friendly manner?
The leak detector for inspection work on the
vehicle –
A possible cause of insufficient cooling output is
loss of coolant due to leaky lines.
Minor leaks (external damage) can only be
verified by means of suitable leak detecting
equipment, due to the minute quantity of
refrigerant which is discharged. Leaks with less
than 5 grammes of refrigerant loss per annum
can be detected using this equipment.
The equipment developed specially for air
conditioners conforms to these requirements.
This equipment is expensive, however, and is
therefore not available nationwide rather only at
service station for air conditioners.
Working on the refrigerant circuit calls for
– a special knowledge of proper
repairs
– a knowledge of the safety regulations and the
Pressure Vessel Code
– verification of appropriate qualifications
(country-specific).
This specialist personnel at the service station for
air conditioners meet the above requirements.
66
208_014
Page 67
An all-in-one system for checking, drawing
off, evacuating and filling
– the Service Recycling Station
This station meets all the requirements relating to
the maintenance, testing and commissioning of
vehicle air conditioners in refrigeration terms.
Various makes of station are available.
A station comprises various individual units:
Filling cylinder, pressure gauges, vacuum pump,
shut-off valve, filling hoses.
Quick-connect adapters for the service
connections in the high- and low-pressure areas
of the refrigerant circuit.
The stations can be used to empty, evacuate and
fill the vehicle air conditioner.
The extracted refrigerant is recycled (dried and
cleaned by removing suspended matter) in the
station and refilled after being repaired.
208_113
Under the government ordinance
For refrigerant disposal
– the recycleable bottle
Refrigerant which contains excessive amounts of
impurities, e.g. due to internal mechanical
damage to the compressor, should not be
cleaned. This refrigerant is drawn off in a
separate extractor station with a recycleable
bottle, which is evacuated on delivery and then
disposed of.
Recycleable bottles may only be filled up to 75 %
of the specified filling weight (expansion of the
refrigerant upon exposure to heat must be
possible). Therefore, they must be weighed using
a calibrated weigher while being filled (observe
the Pressure Vessel Code).
prohibiting the use of CFCs and halogens,
it is not permitted to perform work on air
conditioners without the recycling station.
Recycling stations may only be operated by
expert personnel.
208_086
67
Page 68
Technical Service
General information on function
influencing factors
Mechanical faults (e.g. damage to the
compressor) can reduce the cooling capacity of
the air conditioner, as can chemical or physical
influences.
The refrigerant in particular can have an effect
on the functioning of the air conditioner by virtue
of its properties. Therefore, a knowledge of
general relationships is also important to
everyday servicing, and not only for the
specialists working at the service station for air
conditioners.
Refrigerant and moisture
Only small amounts of water can be dissolved in
the liquid refrigerant. However, refrigerant
vapour and water vapour will mix in any
proportion.
If the drier in the fluid tank or collecting tank has
already absorbed 6 - 12 grammes of water,– i.e.
a relatively small quantity, – it may not function
properly depending on type. Any existing water
is entrained into the refrigerant circuit. This water
reaches the nozzle of the expansion valve or the
restrictor and freezes.
This will reduce the cooling output of the air
conditioner.
Water will damage the air conditioner
irreparably because it combines with other
impurities to form acids at high pressures and
high temperatures.
Refrigerant + refrigerant
Refrigerants may not be mixed with one another
(their chemical and physical properties are
different and they contain different oils).
Only the refrigerant specified for a particular air
conditioner may be used.
Air conditioners which can no longer be supplied
with R12 according to the ordinance prohibiting
the use of halogens must be converted in
compliance with special guidelines.
H
RR
RR
RR
RR
111133
2
111122
++
++
33
O
22
44
44
aa
aa
68
Page 69
Refrigerants and plastics
Refrigerant can dissolve certain plastics. These
dissolved plastics can be deposited in the
expansion valve or at the restrictor after they
cool down.
The valve will become obstructed.
Therefore, always use original spare parts at
seals.
Refrigerants and metals
Refrigerant R134a is chemically stable in its pure
state. It does not attack iron and aluminium.
Contamination of the refrigerant, e.g. with
compounds of chlorine, however, can lead to
certain metals and plastics being attacked. This
can result in obstruction, leaks or deposits at the
compressor piston. Therefore, always use R134a
compatible original spare parts.
208_120
Always use original spare parts.
For this reason, air conditioners can only be
converted from refrigerant R12 to R134a,
including refrigerant oil, according to special
guidelines of the manufacturer (retrofit-process).
Refrigerant circuit and impurities
A refrigerant circuit filled with refrigerant R134a
can be cleaned:
in order to remove impurities, moisture or old
refrigerant, the refrigerant circuit is cleaned with
dried compressed air and then demoisturised
with nitrogen.
This is necessary when
– the refrigerant circuit was opened during its
normal lifetime (e.g. after an accident),
– there is doubt regarding the amount of refri-
gerant oil contained in the circuit,
– the compressor has to be replaced due to
internal damage.
Conversion from
refrigerant R12 to R134a
208_121
The gas mixture emerging from component parts
of the refrigerant circuit must be drawn off using
workshop suction apparatus.
69
Page 70
Technical Service
Fault diagnosis through pressure
testing
For service work, there are terminals for the
Service Recycling Station in the low-pressure and
high-pressure ranges
– for filling
– for emptying
– for evacuating and
– for pressure testing.
To perform a pressure test, the pressure gauges
of the station are connected. The pressure test is
performed with the air conditioner switched on.
A pressure test involves intervening in
the refrigerant circuit via the service
connections.
The hoses of the pressure gauges will
always contain residual refrigerant.
Therefore, pressure tests may only be
performed at air conditioner service
points by specialist personnel.
The ambient temperature when the engine is not
running always affects the pressure in the
refrigerant circuit.
High-pressure service connection
Tolerance range
2,3
2,2
bar
2,1
2,0
1,9
1,8
1,7
1,6
Low pressure
Tolerance range of
1,5
system with restrictor
1,4
0
0 5 7,5 10 12,5 15 17,5 20
of system with expansion valve
High pressure
208_010
bar
208_104
70
Using the test data for the high-pressure side
and the low-pressure side, the system can
identify whether an air conditioner is operating
properly when the engine is running.
The measured values must be compared with
the test data of the vehicle-specific refrigerant
circuit according to the Workshop Manual, as
they vary greatly from one vehicle type to
another.
The pressure diagrams show the tolerance
ranges for systems with an expansion valve and
systems with a restrictor.
208_011
Low-pressure service connection
Page 71
Fault diagnosis through self-diagnosis
Not all air conditioners have self-diagnostic
capability.
Self-diagnosis is used very little in the case of
manual air conditioners (they have either no or
very few sensors/actuators/control units).
In some manual air conditioners, however, the
circuit for the compressor and the sensors of the
safety cut-out are registered by the selfdiagnosis.
Automatic air conditioners with control units
usually have self-diagnostic capability.
The address word for the self-diagnosis:
08 - Air conditioner/heating electronics
202_002
Self-diagnosis can be performed with
Vehicle Diagnostic, Testing and Information
System VAS 5051,
with Vehicle Systems Tester V.A.G 1552 or with
Fault Reader V.A.G 1551.
Faults which impair the operation of an
automatic
air conditioner are stored in the fault memory of
the air conditioner control unit.
In some systems, e.g. CLIMATRONIC, faults of
this type are indicated on the display unit when
the ignition is switched on (all the symbols flash
for several seconds).
The self-diagnosis functions and the
self-diagnosis procedure are explained
in detail in the Workshop Manual
for the heating and air conditioning
system of the vehicle type.
Self-diagnosis can be performed by any
workshop, because the refrigerant
circuit is not affected by this procedure
(i.e. it is not opened).
208_122
71
Page 72
Information
Key cooling system terminology
The cooling system air-conditions the vehicle
interior using the laws of physics. A chemical
medium, the refrigerant, is used for heat
exchange.
Heat ➝
Cold ➝
Critical point ➝
an energy form – measurable by the temperature in degrees
states can change = slight temperature rise (heat absorption)
or = slight temperature decrease (heat dissipation)
is in fact only a low degree of heat.
Temperatures below the freezing point of water
are generally referred to as cold.
above this point, there is no interface between liquid and vapour. A
substance is always in a vapour state above the critical point. If a gas is
heated above the critical point, liquefaction will no longer be possible.
The principles of cooling engineering are
easier to understand with a knowledge of the key
terms:
– by the quantity of energy in Joules (calories)
can be stored or
= always propagates towards
lower temperatures.
Boiling point ➝
Dew point ➝
Condensation ➝
Refrigerant ➝
Cooling
through ➝
expansion
The temperature at which a substance changes from a liquid to a gas. The
boiling point is pressure-dependent; the boiling point increases as pressure
increases.
the temperature at which the saturation point is reached as the result of
cooling of a gas with a specific water vapour content. When the gas cools
down further, some of its vapour content precipitates on the cooling surface
in the form of a "condensate“.
this time the change of state is from a gas to a liquid.
the chemical medium used for the heat exchange process.
Depending on the pressure and temperature
conditions, the refrigerant exists in a gaseous or liquid state in the air
conditioner. The refrigerant cools down when it expands.
if pressurised gas can suddenly expand via a valve,
–– it will cool down in the process, e.g. when deflating the tyres.
The pressurised air flowing out of the valve is cool.
72
Page 73
Water vapour content of the air
Saturation quantity of water vapour in air at
100% relative humidity and normal air pressure
Temperature
o
C
Quantity
(g/m3)
-5 3.25
0 4.85
5 6.80
10 9.41
15 12.84
18 15.39
19 16.32
20 17.32
21 18.35
22 19.44
23 20.61
24 21.81
25 23.07
26 24.41
27 25.79
28 27.26
30
25
3
g/m
20
15
10
Saturation quantity
5
0
-10 -5 0 5 10 15 20 25 30
Temperature
°C
Absolute
atmospheric ➝
humidity
Relative
atmospheric ➝
humidity
re table ➝
208_103
3
(g/m
) is the water content in 1 m3 of air.
given in %, the ratio of water vapour quantity in the air to max. possible
water vapour quantity in air.
3
The table shows how many g of water per m
the air can hold at various
temperatures. 100% saturation is shown. The higher the temperature, the
larger the quantity of water in the air.
The rule of thumb is: at a temperature of 10 to 30
air in g/m
3
is roughly the same as the temperature in oC.
o
C, the water content in the
73
Page 74
74
Page 75
75
Page 76
Service.
208
Thermosphere
Ozono
sphere
Troposphere Stratosphere
For internal use only © VOLKSWAGEN AG, Wolfsburg
All rights reserved. Technical specifications subject to change without notice.
940.2810.27.20 Technical status: 12/98
❀ This paper is produced from
non-chlorine-bleached pulp.
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