The 2019 Audi A8 Climate Control Systems
eSelf-Study Program 980193

Audi of America, LLC
Service Training
Created in the U.S.A.
Created 5/2018
Course Number 980193

©2018 Audi of America, LLC
All rights reserved. Information contained in this manual is based on
the latest information available at the time of printing and is subject to
the copyright and other intellectual property rights of Audi of America,
LLC., its affiliated companies and its licensors. All rights are reserved to
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be referred to Audi of America, LLC.
Always check Technical Bulletins and the latest electronic service repair
literature for information that may supersede any information included
in this booklet.

Revision:May 25, 2018
ii

Introduction

1

The new R744 refrigerant
Global Warming Potential

2
4

Design of the R744 refrigerant system

5

Schematic diagram and function description
AC compressor
Gas cooler
Internal heat exchanger
Pressure relief valve, low and high-pressure sides
Expansion valve
Accumulator
Refrigerant lines
Refrigerant pressure and temperature sensors G1052 / G1053
Vehicle Interior Carbon Dioxide Concentration Sensor G929
Components of the R744 refrigerant circuit
Topology

5
6
7
8
9
10
11
12
14
15
16
18

Air quality and freshening quality

20

Interior fragrance system
Air improvement system

20
21

AC control panels in the front and rear

22

Front area
Rear area

22
24

Seats and available functions

26

Massage function
Surface heating
Foot heater
Optional seat heating and ventilation

26
28
29
29

Workshop equipment

30

A/C service station
Service connections

30
31

Appendix

32

eSelf-Study programs

32

Knowledge assessment

The eSelf-Study Program (eSSP) teaches a basic understanding of the design and mode of operation of new models, new
automotive components or new technologies.

33

Note

It is not a repair manual! Figures are given for explanatory purposes only and refer to the data valid at the time of
preparation of the SSP.
For further information about maintenance and repair work, always refer to the current technical literature.

Reference
iii

iv

Introduction
The climate control system of the 2019 Audi A8 will mark the
introduction of a new refrigerant as well as new in-car air
quality enhancements.
The new refrigerant is carbon dioxide-CO2. It has different
physical properties than other refrigerants in use. For
example, it is non-flammable, colorless and odorless.
Because a carbon dioxide charged system will operate at much
higher pressures, the components of the refrigerant system
have been adapted.

The new refrigerant will only be offered in Europe at the
launch of the 2019 A8. The dates for implementation in the
US have not been determined at the time of the release of
this SSP.
For the North American market, the 2019 A8 will use refrigerant R-1234yf at vehicle introduction.
The new 2019 also offers air quality features such as a cabin
fragrance system and an air improvement system.

665_002

Learning objectives of this eSelf-Study Program:
This eSelf-Study Program describes the new features of the
climate control system in the 2019 Audi A8, as well as the
design and function of the refrigerant system filled with
the new R744 refrigerant introduced in this model. Once
you have completed this eSelf-Study Program you will be
able to answer questions on the following topics:

›› How is the air conditioning system configured for use of the
new R744 refrigerant?
›› What are the points to note when servicing the cabin fragrance system function unit?
›› What are the new display and control features of the air
conditioning system?
›› What new massage functions are available in the new Audi
A8?
1

The new R744 refrigerant
The new refrigerant is carbon dioxide. It has the chemical
formula CO2 and is also known as R744. It contains neither
fluorine nor chlorine and is produced in a series of natural
processes without the possibility depleting the Earth's
ozone layer.
CO2 is a colorless, non-flammable gas and is chemically
slow to react with with other elements. Carbon dioxide is
heavier than air. It is a naturally occurring substance which
is available at an affordable price.

CO2 based refrigerant systems operate at 10 times the
pressure of systems filled with the refrigerants used previously.
The system has to be sealed more tightly because CO2 molecules are smaller than the molecules of other refrigerants.
R744 refrigerant is a natural substance. It may be discharged into the environment and is not subject to the
documentation requirements which apply to chemical
refrigerants.

In the event that the refrigerant circuit should incur a leak,
the refrigerant can enter the atmosphere without causing
damage to the environment.
Carbon dioxide can exist in solid, liquid, gaseous and supercritical states, but it only occurs in gaseous, liquid and
supercritical states in automotive refrigerant systems
systems.

Features
Chemical formula

CO²

Chemical name

Carbon dioxide

Boiling point at 14.5 psi (1 bar) (absolute pressure)

109.6 °F (-78.7 °C)

Freezing point

-69.8 °F (-56.6 °C)

Triple point – Pt

-69.8 °F (-56.6 °C) at 75.4 psi (5.2 bar) (absolute)

Critical point – Pc

87.8 °F (73.8 bar) at 73.8 bar (absolute)

Purity (for refrigerant circuits in Audi models)

>99.995 %

Flammability

Non-flammable

Form

Compressed, liquefied gas

Color

Colorless

Odor

No inherent odor

Note
The new refrigerant will only be offered in Europe at launch. The dates for implementation in the US have not been determined at the time of the release of this SSP. about not available at launch.

Note
The R744 refrigerant odes not have an inherent odor and therefore is not noticeable. However, the refrigerant gas is heavier
than air and can accumulate in lower-lying areas such as inspection pits, basement rooms, where it displaces the ambient air
and oxygen. Working in areas with a low oxygen level can have life-threatening consequences.

2

Phase diagram for carbon dioxide – CO₂

CO2 (s)

CO2 (sc)

CO2 (l)

Pc

73.8

Pressure in bar

CO2 (g)
5.2

Pt

1.0
665_022

-78.7

-56.6

31.1

Temperature in SDgrC

The phase diagram showing the solid (s), liquid (l), gaseous (g) and
supercritical (sc) phases of carbon dioxide is not to scale.

Properties of the R744:
A supercritical situation can occur in the R744 refrigerant
circuit. The critical point is when a substance enters a
thermodynamic state, where the densities of the liquid and
gas phases become equal and the distinction between
them disappears. In a supercritical situation, the state of
the refrigerant in the gas cooler does not change from
gaseous to liquid state, but rather is cooled only. Hence the
term "gas cooler".

Due to the higher energy content of CO2, a lower mass flow
rate is required in order to achieve the same refrigerating
capacity. In addition to increasing the refrigerating capacity
of the system, this advantage can be used to realize a more
compact unit design and to reduce the flow component
cross-sections.

3

Global Warming Potential
The Global Warming Potential (GWP) describes the relative
global warming effect of a greenhouse gas, that is, how
much a gas potentially contributes to the warming of the
Earth's atmosphere.
The reference value used as the basis for comparison is that
of carbon dioxide (CO2), which has a GWP of one. The
smaller the GWP value, the lesser the potential global
warming effect and, by implication, the less the impact on
the environment.

Starting from 1 January 2017, vehicles using a refrigerant
with a GWP value of greater than 150 cannot be type-approved in European Union countries. For this reason, the
use of refrigerants such as R134a is prohibited in these
countries.
For this reason, Audi has been using the R1234yf refrigerant
as standard since 2016 in many countries. With the launch
of the new Audi A8, carbon dioxide is available as an alternative refrigerant.

For example, R1234yf has a GWP of four for a time
horizon of 100 years. This means that one kilogram of
R1234yf has four times the global warming effect of one
kilogram of CO2 within the first 100 years after its release
into the environment.

Properties of the various refrigerants

4

Refrigerant

R12
(CFCs)

R134a
(HFCs)

R1234yf
(HFCs)

R744
(CO₂)

Ozone layer
depletion

Yes

No

No

No

Global Warming Potential
(GWP)

About 10,000x
that of CO₂

About 1,400x
that of CO₂

About 4x
that of CO₂

1x

Year of use in vehicle

Up to 1992

From 1991 onwards

From 2016 onwards

US date TBD

Refrigerant type

Synthetic

Synthetic

Synthetic

Natural

Flammable

No

No

Yes

No

Pressure

< 435.1 psi (30 bar)

< 435.1 psi (30 bar)

< 435.1 psi (30 bar)

< 2030.5 psi (140 bar)

Design of the R744 refrigerant system
Schematic diagram and function description
The key difference to the previously used refrigerant systems is the high working pressures. Higher pressures are required to
make use of C02 as a refrigerant. R744 will operate at a pressure of about 2030.3 psi (140 bar) on the high pressure side of
the circuit and about 1348.8 psi (93 bar) on the low pressure side.

High Pressure Side A/C Pressure/Temperature Sensor
G1053

Gas cooler

Service connection
High pressure
Internal heat exchanger

Service connection
Low pressure

Expansion valve

Pressure relief valve
Low-pressure side
Low Pressure Side A/C
Pressure/Temperature
Sensor
G1052

Evaporator

Pressure relief valve
High-pressure side
Compressor

Accumulator
665_023

Component designation

Processes in the refrigerant circuit

Compressor

Compression of gaseous CO₂ to a higher pressure level

Gas cooler

Cooling of the refrigerant

Internal heat exchanger

Heat is dissipated in the internal heat exchanger. Heat is transferred from the high-pressure
side to the low-pressure side.

Expansion valve

When refrigerant expands in the expansion valve, the pressure is reduced by restricting
the flow.

Evaporator

The refrigerant absorbs energy from the air flowing through the evaporator.

Accumulator

The accumulator dries and stores the refrigerant and provides a place for the oil and
refrigerant to mix.

Internal heat exchanger

Heat is absorbed in the internal heat exchanger. Heat is transferred from the high-pressure
side to the low-pressure side.

5

AC compressor
The AC compressor compresses the gaseous refrigrant so
that it can subsequently be allowed to expand again inside
the evaporator. The expansion of the refrigerant causes the
temperature to drop, allowing heat to be extracted from
the passenger compartment.

plate, the individual pistons move in a reciprocating linear
manner inside their cylinders, with the result that refrigerant is drawn into the compressor, compressed inside the
piston chamber and then pumped into the refrigerant
circuit.

The refrigerant compressor works on the same principle as
an axial piston pump or axial piston compressor, with fixed
pistons spaced at even intervals around the inner circumference of working cylinders and mounted movably on a
rotating swashplate. By following the tilt of the swash-

The tilt angle of the swashplate is variable, and changes
the resultant mass flow. The angle of the swashplate
regulates itself according to the required mass flow.
Specifications of the compressor:
›› 9 pistons.
›› 31 cm³ stroke volume.
›› Mass flow controlled.

Refrigerant line
connection High pressure

Connection to 12-volt
electrical system

Pressure relief valve
High-pressure side
Oil drain bolt

Refrigerant line
connection Low pressure

Belt pulley
with solenoid coupling

A/C Compressor Regulator
Valve N280

665_003

6

Gas cooler
The gas cooler is a newly developed component which takes
the place of the condenser. It cools the refrigerant down.
The gas cooler dissipates process heat of the high pressure
side to the atmosphere. It is designed for both supercritical
operation (as a "gas cooler") and alternating phase operation (as a "condenser"). The term "alternating phase"
defines a refrigerant whose aggregate state alternates
between gaseous and liquid.

The gas cooler is made of flat tubes. Inside the flat tubes,
smaller tubes are bundled longitudinally. The flat tubes
themselves are arranged in a row next to one another. The
refrigerant flows through the gas cooler into the upper
segments and then back to the lower segments in the
opposite direction.
High Pressure Side A/C Pressure/Temperature Sensor
G1053 is located at the gas cooler.

High Pressure Side A/C Pressure/Temperature Sensor
G1053

665_004

7

Internal heat exchanger
The internal heat exchanger is similar to the Coolaxial pipe
used in other Audi model refrigerant systems.
The internal heat exchanger is a tube-in-tube heat
exchanger consisting of an inner high-pressure tube enveloped by low-pressure tubes. The refrigerant flowing
through the low-pressure tubes absorbs heat. In the
high-pressure tube, the refrigerant flowing in the opposite
direction gives off heat. This allows energy to be exchanged
between the low and high-pressure sides.

The principal task of the internal heat exchanger is to
increase the efficiency of the refrigerant circuit. This is
achieved by extending the circulation process to increase
the enthalpy difference at the evaporator. For this purpose,
the internal heat exchanger using refrigerant R744 is
required to be about a yard (meter) long.
Note: Enthalpy is defined as a thermodynamic quantity
equivalent to the total heat content of a system. It is equal
to the internal energy of the system plus the product of
pressure and volume.

Internal heat
exchanger

665_005

High-pressure side

8