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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

6

Basic technical and physical proper‐

ties

⇒ “6.1 Basics of air conditioning technology”, page 16

⇒ “6.2 Physical properties”, page 19

⇒ “6.3 Product characteristics”, page 26

⇒ “6.4 Function and role of air conditioning system”, page 26

⇒ “6.5 Other reference material”, page 28

6.1

Basics of air conditioning technology

⇒ “6.1.1 Physical properties of air conditioning system”,

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page 16

⇒ “6.1.2 Pressure and boiling point of refrigerant”, page 17

⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17

⇒ “6.2 Physical properties”, page 19

6.1.1

Physical properties of air conditioning

system

The 4 familiar states of water apply to air conditioning refrigerants

as well.

1 - Gas (invisible)

2 - Vapour

3 - Liquid

4 - Solid

When water is heated in a vessel (heat absorption), water vapour

can be seen to rise. If the vapour is heated by further heat ab‐

sorption, the visible vapour becomes invisible gas. The process

is reversible. If heat is extracted from gaseous water -A-, it

changes first to vapour -B-, then to water and finally to ice.

A - Heat absorption

B - Heat dissipation

Heat always flows from a warmer to a colder substance

Every substance consists of a mass of moving molecules. The

fast moving molecules of a warmer substance give off some of

their energy to the cooler and thus slower molecules. As a result,

the molecular motion of the warmer substance slows down and

that of the colder substance is accelerated. This continues until

the molecules in both materials are moving at the same speed.

They are then at the same temperature and no further heat ex‐

change takes place.

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6.1.2

Pressure and boiling point of refrigerant

The boiling point given in tables for a liquid is always referenced

to atmospheric pressure (1 bar absolute pressure). If the pressure

over a fluid changes, its boiling point changes as well.

Note

lk

Pressure is indicated in various units: 1 MPa (Mega-Pascal) is

equal to 10 bar or 145 psi; 1 bar absolute pressure is equal to

0 bar, which is about the same as ambient pressure (atmospheric

pressure).

It is well known that e.g. the lower the pressure, the lower the

temperature at which water boils.

The vapour pressure curves for water and for R1234yf refrigerant

show that at constant pressure and falling temperature the vapour

becomes liquid (in the condenser), and that when pressure drops,

for example, the refrigerant changes from liquid into the vaporous

state (in the evaporator).

Vapour curve, water

A - Liquid

B - Gaseous

C - Vapour curve, water

1 - Pressure on the liquid in bar (absolute)

2 - Temperature in °C

Vapour pressure curve for refrigerant R1234yf

A - Liquid

B - Gaseous

D - Vapour pressure curve for refrigerant R1234yf

1 - Pressure on the liquid in bar (absolute)

2 - Temperature in °C

Note

The vapour pressure curves of both refrigerants, R1234yf and

R134a, are very similar across a broad temperature range. The

pressure difference between the two refrigerants in a temperature

range of 0 C to +50°C is only about 0.2 bar, for example, which

is why it is not possible to differentiate between the two refriger‐

ants ⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17

and ⇒ Air conditioning system with R134a refrigerant; Rep. gr.

87 ; General information about the air conditioning system and

refrigerant circuit . It is only possible to determine a difference

using relevant sensors, which can analyse the chemical structure

of the refrigerant

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

6.1.3

Vapour pressure table for refrigerant

The vapour pressure table for every refrigerant is published in

literature for refrigeration system engineers. This table makes it

6. Basic technical and physical properties

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

possible to determine the vapour pressure acting on the column

of liquid in a vessel if the temperature of the vessel is known.

Since its own characteristic vapour pressure table is known for

each refrigerant, it is possible to establish the type of refrigerant

by measuring the pressure and temperature of refrigerants whose

vapour pressure changes over a certain temperature range (does

not apply when differentiating between R1234yf and R134a as

the vapour pressures are too close

⇒ “6.1.2 Pressure and boiling point of refrigerant”, page 17 ).

Note

♦ The means of differentiation are only given for pure refriger‐

ants whose vapour pressures differ sufficiently. If different

refrigerants are mixed for form a new refrigerant (e.g. 3 differ‐

ent refrigerants to form R407C refrigerant), a vapour pressure

will be created in accordance with the vapour pressures of the

individual refrigerants and their percentage in the mixture.

♦ Absolute pressure means that “0 bar” corresponds to an ab‐

solute vacuum. The normal ambient pressure corresponds to

“1 bar” absolute pressure. On most pressure gauges, a read‐

ing of “0 bar” corresponds to an absolute pressure of one bar

(which is confirmed by the existence of a “-1 bar” marking be‐

neath the “0” scale marking).

♦ Pressure is indicated in various units: 1 MPa (Mega-Pascal)

is equal to 10 bar or 145 psi; 1 bar absolute pressure is equal

to 0 bar, which is about the same as ambient pressure (at‐

mospheric pressure).

♦ The vapour pressures of the two refrigerants, R1234yf and

R134a, are very similar across a broad temperature range,

which is why no difference can be established between them

⇒ Air conditioning system with R134a refrigerant, General in‐

formation about the air conditioning system . It is only possible

lk

to determine a difference using relevant sensors, which can

analyse the chemical structure of the refrigerant

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

Temperature in °C

Pressure in bar (positive pres‐

sure) R1234yf

-40

-30

-25

-20

-15

-10

-5

-0.40

-0.01

0.12

0.50

0.83

1.21

1.65

2.15

2.72

3.36

4.09

4.90

5.81

6.82

7.93

9.17

10.52

0

5

10

15

20

25

30

35

40

45

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Temperature in °C

Pressure in bar (positive pres‐

sure) R1234yf

50

55

60

65

70

75

80

85

90

12.01

13.64

15.41

17.35

19.46

21.75

24.24

26.94

29.09

6.2

Physical properties

⇒ “6.2.1 R1234yf refrigerant”, page 19

⇒ “6.2.2 Potential risks with R1234yf refrigerant”, page 20

⇒ “6.2.3 Physical and chemical properties of R1234yf refrigerant”,

page 20

lk

⇒ “6.2.4 Critical point”, page 20

⇒ “6.2.5 Environmental aspects of refrigerant R1234yf”,

page 21

⇒ “6.2.6 Trade names and designations of R1234yf refrigerant”,

page 21

⇒ “6.2.7 Colour and odour of R1234yf refrigerant”, page 22

⇒ “6.2.8 Vapour pressure of R1234yf refrigerant”, page 22

⇒ “6.2.9 Physical properties of R1234yf refrigerant”, page 22

⇒ “6.2.10 How R1234yf refrigerant reacts to metals and plastics”,

page 22

⇒ “6.2.11 Critical temperature / critical pressure of R1234yf re‐

frigerant”, page 23

⇒ “6.2.12 Water content of R1234yf refrigerant”, page 23

⇒ “6.2.13 Flammability / decomposition of R1234yf refrigerant”,

page 23

⇒ “6.2.14 Charge factor of refrigerant R1234yf”, page 23

⇒ “6.2.15 Evidence of leaks in a refrigerant circuit with R1234yf

refrigerant”, page 24

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24

⇒ “6.2.17 Returning contaminated R1234yf refrigerant for analy‐

sis, processing or disposal”, page 25

6.2.1

R1234yf refrigerant

♦ Air conditioners in vehicles employ the evaporation and con‐

densation process. A substance (the refrigerant) is moved

about a circuit within an enclosed system.

♦ The substance is one that has a low boiling point, in this in‐

stance R1234yf refrigerant.

♦ The R1234yf refrigerant is marketed under various names

(e.g. HFO 1234yf, Opteon 1234yf etc.).

6. Basic technical and physical properties

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

lk

♦ For the air conditioning system, only approved refrigerant with

the requisite level of purity may be used

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

♦ R1234yf refrigerant is a halogenated hydrocarbon compound

with the chemical designation “2,3,3,3-tetrafluoroprop-1-ene”

which boils at -29.4°C at a vapour pressure of “1 bar” (equiv‐

alent to ambient pressure).

6.2.2

Potential risks with R1234yf refrigerant

♦ The refrigerant is flammable with ambient air in a certain mix‐

ture ratio

⇒ “6.2.3 Physical and chemical properties of R1234yf refrig‐

erant”, page 20 and

⇒ “6.2.13 Flammability / decomposition of R1234yf refriger‐

ant”, page 23 .

♦ Rapid vaporisation of the liquid can cause freezing injuries

♦ High vapour concentrations can cause headaches, dizziness,

drowsiness and nausea and even loss of consciousness.

6.2.3

Physical and chemical properties of

R1234yf refrigerant

The following is a list of the main properties and safety information

for R1234yf refrigerant. The complete details can be found in the

respective safety data sheets on the ⇒ VW / Audi ServiceNet .

Chemical formula

CF3CF=CH2

Chemical designation

2,3,3,3-tetrafluoroprop-1-ene,

HFO-1234yf

Boiling point at 1 bar

Solidification point

Critical temperature

Critical pressure

-29.4 °C

-152.2 °C

94.7 °C

32.82 bar (positive pressure)

33.82 bar (absolute pressure)

Self-combustion temperature 405°C at 1.02 bar (absolute

pressure)

Flammability

Flammable gas

♦ Lower explosion threshold

6.2% (volume)

♦ Upper explosion threshold

12.3% (volume)

Form

Colour

Odour

Compressed, liquefied gas

Colourless

Weak odour

6.2.4

Critical point

The critical point (critical temperature and critical pressure)

means the point above which there is no longer a surface of sep‐

aration between liquid and gas.

A substance above its critical point is always in the gaseous state.

At temperatures below the critical point, all types of refrigerant

contained within a pressure vessel exhibit a liquid phase and a

gas phase, i.e. there is a gas cushion above the liquid.

As long as there is gas in the pressure vessel alongside the liquid,

the pressure depends directly on the ambient temperature

⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17 .

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Note

♦ Refrigerants used in motor vehicles must not be mixed to‐

gether. Only the refrigerant prescribed for the respective air

conditioning system may be used.

♦ The vapour pressures of the two refrigerants, R1234yf and

R134a, are very similar across a broad temperature range,

which is why no difference can be established between them

⇒ Air conditioning system with R134a refrigerant, General in‐

formation about the air conditioning system . It is only possible_lk

to determine a difference using relevant sensors, which can

analyse the chemical structure of the refrigerant

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

6.2.5

Environmental aspects of refrigerant

R1234yf

♦ R1234yf is a fluorocarbon (FC) and contains no chlorine.

♦ R1234yf has a shorter atmospheric life than R12 and R134a

refrigerant and therefore has a less significant greenhouse ef‐

fect (lower global warming potential).

♦ R1234yf does not damage the ozone layer, the potential to

reduce the amount of ozone is zero (as is the case with

R134a).

♦ The global warming potential (GWP) of R1234yf is 4 (the GWP

for carbon dioxide is 1).

♦ The contribution of R1234yf towards global warming is lower

than the R134a refrigerant by a factor of “350” (GWP of R134a

is about 1400).

Note

♦ The global warming effect of substances is calculated accord‐

ing to various methods based on their effect over a period of

100 years, which is why the results differ (e.g. R134a has a

GWP between 1300 and 1450).

♦ In order to compare the impact of various greenhouse gases

on the earth atmosphere, a calculation is carried out using the

carbon dioxide equivalent. The refrigerant R1234yf has a

GWP of 4, i.e. 1 kg of this refrigerant has the same impact on

the earth atmosphere as 4 kg of carbon dioxide (“CO ”).

2

6.2.6

Trade names and designations of

R1234yf refrigerant

Refrigerant R1234yf is currently available under the following

trade names:

♦ H-FKW 1234yf

♦ HFO 1234yf

♦ “Opteon yf” or“ Solstice yf” (examples of company names)

6. Basic technical and physical properties

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Note

♦ Different trade names may be used in other countries.

♦ Of the wide range of refrigerants available, this is the only one

which may be used for vehicles. The names Frigen and Freon

are trade names. These also apply to refrigerants which are

not to be used in vehicles.

6.2.7

Colour and odour of R1234yf refrigerant

♦ Like water, refrigerants are colourless in both vapour and liq‐

uid form. Gas is invisible. Only the boundary layer between

gas and liquid is visible (liquid level in indicator tube of charg‐

ing cylinder or bubbles in sight glass). Liquid refrigerant

R1234yf may have a coloured (milky) appearance in a sight

glass. This cloudiness is caused by partially dissolved refrig‐

erant oil and does not indicate a fault.

♦ Refrigerant is almost odourless. Should R1234yf refrigerant

escape, it may be possible to detect a slight smell of ether

depending on the ambient conditions.

6.2.8

Vapour pressure of R1234yf refrigerant

In an enclosed container that is not completely full, refrigerant

evaporates at the surface in a quantity sufficient to form an equi‐

librium between vapour and liquid. This state of equilibrium occurs

under the influence of pressure and is often called vapour pres‐

sure. The vapour pressure is temperature-dependant

⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17 .

6.2.9

Physical properties of R1234yf refriger‐

ant

♦ The vapour pressure curves of the two refrigerants, R1234yf

and R134a, are very similar across a broad temperature

range, which is why no difference can be established between

them

⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17 and

⇒ Air conditioning system with R134a refrigerant, General in‐

formation about the air conditioning system . It is only possible

to determine a difference using relevant sensors, which can

analyse the chemical structure of the refrigerant

⇒ “6.2.16 Analysis of refrigerant R1234yf”, page 24 .

♦ Lubrication of the air conditioner compressor with R1234yf is

by special synthetic refrigerant oils, e.g. PAG oils (polyalky‐

lene glycol oils) with certain additives adapted to the R1234yf

refrigerant oil, the air conditioner compressor and the operat‐

ing conditions.

6.2.10

How R1234yf refrigerant reacts to met‐

als and plastics

♦ In its pure state, R1234yf refrigerant is chemically stable and

has no corrosive effect on e.g. iron, aluminium and specially

developed plastics that are suitable for this purpose.

♦ Contaminants in the refrigerant, however, cause components

of the refrigerant circuit to become corroded and damaged

beyond repair.

♦ Unsuitable materials (e.g. seals and hoses that were not de‐

veloped for the R1234yf refrigerant and the associated refrig‐

erant oil) can also be corroded and damaged by pure R1234yf

refrigerant and refrigerant oil.

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♦ If the refrigerant is contaminated, e.g. with chlorine com‐

pounds or by the influence of UV light, metals and also plastics

developed and tested for this refrigerant and refrigerant oil can

be corroded. This can lead to blockages, leaks and deposits

on the air conditioner compressor piston.

lk

♦ Certain metals can be corroded by R1234yf refrigerant (e.g.

finely distributed aluminium, zinc, magnesium)

6.2.11

Critical temperature / critical pressure of

R1234yf refrigerant

Up to a gas pressure of 32.82 bar (which is equivalent to a tem‐

perature of 94.7°C), refrigerant evaporates at the surface in a

quantity that, combined with particles of vapour, returns it to liquid

again. Above this temperature / pressure there is no longer a sur‐

face separating the liquid and gas.

6.2.12

Water content of R1234yf refrigerant

♦ Only very small amounts of water are soluble in liquid refrig‐

erant. On the other hand, refrigerant vapour and water vapour

mix in any ratio.

♦ Any water in the refrigerant circuit will be entrained in droplet

form once the dryer in the receiver or reservoir is full (once it

has absorbed approx. 7 g of water). This water flows as far as

the expansion valve nozzle or the restrictor and turns to ice.

The air conditioner no longer provides cooling.

♦ If the existing water at the regulating valve of the air conditioner

compressor turns to ice, a variety of complaints may be made

depending on the design of the air conditioner compressor

(either the air conditioning system stops cooling or the air con‐

ditioning system cools to such a degree that the evaporator

ices over).

♦ Water destroys the air conditioner because at high pressures

and temperatures it can combine with other impurities to form

acids.

6.2.13

Flammability / decomposition of

R1234yf refrigerant

♦ In certain concentrations in the ambient air, R1234yf refriger‐

ant is flammable.

♦ R1234yf begins to decompose when exposed to flames and

glowing or hot surfaces. Even UV light causes refrigerant to

break up (UV light is part of normal sunlight, it is also encoun‐

tered e.g. during electrical welding), which releases poisonous

fission products that must not be inhaled. However, these

chemicals irritate the mucous membranes, giving adequate

warning of their presence.

♦ During decomposition, certain hazardous products such as

carbon monoxide, hydrogen fluoride and / or hydrogen halide

can be released.

6.2.14

Charge factor of refrigerant R1234yf

♦ When charging compressed gas containers (returnable cylin‐

ders, recycling cylinders etc.), observe the applicable regula‐

tions, technical rules and legislation.

♦ Never overcharge compressed gas containers (returnable cyl‐

inders, recycling cylinders etc.). The gas cushion (expansion

space) of overcharged compressed gas containers is too

small to accommodate expansion of the fluid caused by a rise

in temperature. Risk of bursting.

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♦ To ensure safety, only use compressed gas containers fitted

with a safety valve.

♦ Returnable and recycling cylinders must be weighed on suit‐

able scales during charging, or a method of charging by vol‐

ume must be employed to ensure that the permissible weight

of the filling specified on the tank/container is not exceeded.

The maximum permissible filling volume is 80% of the maxi‐

mum refrigerant volume of the filling weight specified on the

returnable and recycling cylinder or 70% of the maximum filling

volume (charge factor, the smaller of the values always ap‐

plies respectively). Reason: There is no way of absolutely

lk

ruling out refrigerant oil being filled into the returnable and re‐

cycling cylinder along with the refrigerant.

♦ There must be space both for liquid and vapour in a container.

As the temperature rises, the liquid expands. The vapour-filled

space becomes smaller. At a certain point, there will only be

liquid in the vessel. Beyond this, even a slight increase in tem‐

perature causes great pressure to build up in the vessel as the

liquid attempts to continue expanding despite the absence of

the necessary space. The resultant force is sufficient to rup‐

ture the vessel. To prevent containers from being over‐

charged, regulations governing the storage of compressed

gases specify how many kilograms may be charged into a

container for every litre of container volume. This charge factor

multiplied by the internal volume gives the permissible charge

quantity. The charge factor for refrigerant used in vehicles is

1.15 kg/litre.

♦ Since contaminated refrigerant could have a different density

than pure R1234yf refrigerant, the maximum permissible

charge factor must always be observed.

6.2.15

Evidence of leaks in a refrigerant circuit

with R1234yf refrigerant

♦ The refrigerant circuit could develop leaks, for example, from

the use of unsuitable or contaminated refrigerant or untested

materials in unsuitable components.

♦ Since a small leak will involve only small quantities of refrig‐

erant, evidence of leaks should be sought using an electronic

leak detector or by introducing a leak detection additive to the

refrigerant circuit. Electronic leak detectors can detect leakage

rates of less than 5 grams loss of refrigerant per year.

Note

Use must however be made of leak detectors designed for the

composition of the respective refrigerant. For example, leak de‐

tectors for R12 refrigerant are not suitable for R1234yf refrigerant

as these leak detectors do not always respond. Even leak detec‐

tors that are designed just for R134a refrigerant are not suitable

for R1234yf refrigerant because R1234yf refrigerant has a differ‐

ent chemical structure than R134a. Subsequently, these leak

detectors only respond to high concentrations of refrigerant in the

air or not at all ⇒ Electronic parts catalogue .

6.2.16

Analysis of refrigerant R1234yf

For operation of the air conditioning system, it is important that

the refrigerant used has a certain degree of purity.

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Note

♦ A faulty gas analysis is possible from air in the refrigerant ho‐

ses or non-observance of the procedure for gas analysis as

detailed in the operating instructions.

♦ Carefully follow the operating instructions of the gas analysis

device / air conditioner service station .

♦ Evacuate refrigerant hoses of the air conditioner service sta‐

tion before connecting the service couplings to the refrigerant

circuit / gas cylinder with R1234yf refrigerant hose (see oper‐

ating instructions of gas analysis device / air conditioner serv‐

ice station

⇒ “2.3 Performing gas analysis of refrigerant”, page 134 .

Contamination with other refrigerants or gases can cause dam‐

age and thereby failure of the air conditioning system and air

conditioner service station .

Contaminated refrigerant must be analysed and then processed

(or disposed of) as gas of unknown composition in accordance

with the relevant legal requirements

⇒ “2.3 Performing gas analysis of refrigerant”, page 134 .

Note

lk

Return contaminated R1234yf refrigerant to your refrigerant sup‐

plier for analysis. If, owing to refrigerant circuit damage that has

already occurred or is expected, it is necessary for you to know

exactly which impurities the refrigerant is contaminated with, sub‐

mit an application and request analysis results

⇒ “6.2.17 Returning contaminated R1234yf refrigerant for analy‐

sis, processing or disposal”, page 25 .

The following thresholds apply for clean R1234yf refrigerant dur‐

ing the gas analysis:

♦ The extracted refrigerant gas consists of at least 95% R1234yf

refrigerant.

♦ The percentage of impurities (oxygen, nitrogen, vapour, other

refrigerants) is less than 5%.

Note

To prevent liquid components (e.g. droplets of refrigerant oil) in

the extracted refrigerant gas from falsifying the result of the gas

analysis, separators (filters) are installed in the gas analysis de‐

vice that separate these droplets of liquid. Renew filters in ac‐

cordance with the specifications in the operating instructions

accompanying the gas analysis device and air conditioner service

station ⇒ Operating instructions of gas analysis device or ⇒ Op‐

erating instructions of air conditioner service station .

6.2.17

Returning contaminated R1234yf refrig‐

erant for analysis, processing or dispos‐

al

♦ When returning contaminated refrigerant for analysis, pro‐

cessing/recycling or disposing of refrigerant that is no longer

usable, the legal requirements must be observed

⇒ “2 Legal texts and regulations”, page 5 and ⇒ VW / Audi

ServiceNet .

6. Basic technical and physical properties

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♦ When disposing of refrigerant oil that is no longer usable, the

legal requirements must be observed

⇒ “2 Legal texts and regulations”, page 5 and ⇒ VW / Audi

ServiceNet .

♦ To protect the environment, no refrigerant should be released

into the atmosphere

⇒ “2 Legal texts and regulations”, page 5 .

♦ If, during the gas analysis, it is found that the R1234yf refrig‐

erant is contaminated with a different gas, it must be extracted

from the refrigerant circuit and returned to your gas supplier to

be analysed, processed or disposed of as gas of unknown

composition in accordance with the legal requirements ⇒ VW /

Audi ServiceNet and

⇒ “2.13 Filling contaminated refrigerant in a recycling cylinder

for analysis, processing or disposal”, page 161 .

Note

Return contaminated R1234yf refrigerant to ^ly^kour refrigerant sup‐

plier for analysis. If, owing to refrigerant circuit damage that has

already occurred or is expected, it is necessary for you to know

exactly which impurities the refrigerant is contaminated with, sub‐

mit an application by requesting analysis results

⇒ “2.4 Emptying refrigerant circuit”, page 137 .

6.3

Product characteristics

R1234yf refrigerant used in motor vehicle air conditioning sys‐

tems belongs to the new generation of refrigerants based on

chlorine-free, partially fluorinated hydrocarbons.

With regard to their physical properties, these are refrigerants

which have been liquefied under pressure. These are subject to

the regulations governing pressure vessels and use is only to be

made of approved and appropriately marked containers.

Compliance with specific conditions is required to ensure safe and

proper use ⇒ “1 Safety information”, page 1 .

6.4

Function and role of air conditioning sys‐

tem

⇒ “6.4.1 Principle of operation”, page 26

⇒ “6.4.2 Comfort”, page 27

⇒ “6.4.3 Environmental aspects”, page 27

6.4.1

Principle of operation

♦ The temperature in the passenger compartment depends on

the amount of heat radiated through the windows and con‐

ducted by the metal parts of the body. In order to maintain

comfortable temperatures for the occupants on very warm

days, part of the prevailing heat must be pumped away.

♦ Since heat spreads towards cooler bodies, a unit that can cre‐

ate low temperatures is fitted in the vehicle interior. Within this,

refrigerant is continually evaporated. The heat required to do

this is extracted from the air flowing through the evaporator.

♦ The refrigerant carries the heat with it as it is pumped away by

the air conditioner compressor. The work performed by the air

conditioner compressor on the refrigerant increases its heat

content and its temperature. This is now substantially higher

than that of the surrounding air.

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♦ The hot refrigerant flows with its heat content to the condenser.

Here, the refrigerant dissipates its heat to the surrounding air

via the condenser due to the temperature gradient between

the refrigerant and the surrounding air.

♦ The refrigerant thus acts as a heat transfer medium. As it is to

be re-used, the refrigerant is returned to the evaporator.

♦ For this reason all air conditioning systems are based on the

refrigerant circulation principle. There are however differences

in the composition of the units

⇒ “1.1 System overview - refrigerant circuit”, page 30 .

6.4.2

Comfort

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♦ A basic requirement for concentration and safe driving is a

feeling of comfort in the passenger compartment. This comfort

is only reached by using an air conditioning system, particu‐

larly when it is hot and humid. Of course, open windows, an

open sunroof or increased air ventilation can contribute to

comfort, but they all have certain disadvantages within the ve‐

hicle interior, such as additional noise, draughts, exhaust

gases, unhindered entry of pollen (unpleasant for allergy suf‐

ferers).

♦ A well regulated air conditioning system in conjunction with a

well thought-out heating and ventilation system can create a

feeling of well-being and comfort by regulating the interior

temperature, humidity and rate of air change, regardless of the

external conditions. This must be available whether the vehi‐

cle is moving or not.

Other important advantages of air conditioning are:

♦ Drying of the air in the passenger compartment (humidity in

the air condenses on the cold evaporator and is drained away

as condensate, the air is heated up again on the heat ex‐

changer for heater to a preset temperature, which reduces the

water content in the air and the absolute and relative humidity

is reduced).

♦ Additional cleansing of the air directed into the passenger

compartment (dust and pollen that have made their way

passed the dust and pollen filter, for example, are washed out

by the moist fins of the evaporator and carried off with the

condensation water.)

♦ Temperatures in a mid-range car (for example, after a short

period of driving, ambient temperature 30°C in the shade and

the vehicle in direct sunlight).

With air conditioning Without air condi‐

tioning

Head height

Chest

Footwell

23 °C

24 °C

30 °C

42 °C

40 °C

35 °C

6.4.3

Environmental aspects

♦ Until about 1992, air conditioning systems were equipped with

refrigerant R12. Due to its chlorine atoms, this CFC had a high

potential for destroying ozone and, in addition, a very high po‐

tential for increasing the greenhouse effect.

♦ From 1992, the air conditioning systems of newly manufac‐

tured cars have been successively changed from R12 refrig‐

erant to R134a refrigerant. This refrigerant contains no

chlorine and therefore does no damage to the ozone layer.

Due to the high global warming potential of approx. 1400

(GWP), it may no longer be used in vehicles that are newly

type approved from 2011. The cut-off date for bringing vehi‐

6. Basic technical and physical properties

27

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

cles that were type approved before 2011 into operation for

the first time with R134a refrigerant is 31.12.2016 (this applies

to countries within the EU, different regulations may apply in

countries outside the EU).

♦ After 01.01.2011, vehicles will only be given a new type ap‐

proval if the refrigerant used in the refrigerant circuit of their

air conditioning system has a GWP of less than 150. R1234yf

refrigerant has a GWP of approx. 4 and is therefore markedly

below the prescribed level.

♦ From 2011, the air conditioning systems of newly manufac‐

tured cars have been successively changed from R134a re‐

frigerant to R1234yf refrigerant. This refrigerant has a global

warming potential of approx. 4. The GWP of carbon dioxide =

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1 (global warming potential) and has much less of an impact

on the earth’s atmosphere than R134a refrigerant.

♦ Conversion programmes have been developed for old sys‐

tems filled with the ozone-depleting substance R12 ⇒ Work‐

shop manual for air conditioners with R12 refrigerant (this

workshop manual is available in paper form only).

♦ According to current legislation, R134a refrigerant may still be

charged in vehicles that were type approved for use with

R134a refrigerant (or in vehicles converted from R12 refriger‐

ant to R134a refrigerant) until these vehicles are decommis‐

sioned. No provision has currently been made, therefore, to

convert air conditioning systems from R134a refrigerant to

R1234yf refrigerant ⇒ Air conditioning systems with R134a

refrigerant; Rep. gr. 87 ; Capacities for R134a refrigerant, re‐

frigerant oil and approved refrigerant oils .

♦ To protect the environment, no refrigerant should be released

into the atmosphere

⇒ “2 Legal texts and regulations”, page 5 .

♦ R1234yf refrigerant is chemically stable in an enclosed sys‐

tem. In the earth’s atmosphere, however, it decomposes with‐

in a short space of time (within approx. 14 days) by the

influence of UV light into compounds that do not harm the

earth’s atmosphere (hence the GWP of 4).

6.5

Other reference material

♦ Workshop manual for model-specific maintenance work ⇒

Heating, air conditioning system; Rep. gr. 87 ; Overview of

fitting locations - air conditioning system (vehicle-specific

workshop manual) and ⇒ Current flow diagrams, Electrical

fault finding and Fitting locations

♦ Technical Service Handbook with measures for rectifying lat‐

est malfunctions

♦ Self-study Programmes, videos for workshop training and VW/

Audi TV episodes on the air conditioning system.

♦ The specific risks of refrigerant, material data etc. can be

gleaned from the safety data sheets. Safety data sheets about

refrigerant, refrigerant oil etc. ⇒ VW / Audi ServiceNet .

♦ List of relevant special tools and workshop equipment for re‐

pairs to air conditioning systems ⇒ Electronic parts catalogue

(Tools; Workshop equipment/tools; Heating, air conditioning

system).

♦ Information about the disposal of refrigerant oil and contami‐

nated refrigerant can be found on ⇒ VW / Audi ServiceNet .

♦ For vehicles whose refrigerant circuit is charged with R134a

refrigerant (vehicles that were type approved before

31.12.2010 and have been or are to be commissioned for the

28

Rep. gr.00 - Technical data

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

first time by 31.12.2016

⇒ “2 Legal texts and regulations”, page 5 .

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6. Basic technical and physical properties

29

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Technical data -> 6 Basic technical and physical properties for Your Volkswagen Touran 4 Door Second Generation (2015-2022)

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