Low-pressure side

Pressure relief valve, low and high-pressure sides
Protective film

Adjusting screw

Spring

Ball seat
Aluminum housing
Steel ball

Gasket seat

Sensor

665_006

Refrigerant connection

Functional principle
If overpressure occurs in the refrigerant circuit, a steel ball
in the valve is pressed against a spring. This opens passage
which is closed at normal pressure, allowing the refrigerant
to escape.
Both pressure relief valves are reversible valves. The valve is
leak-tested using gas prior to shipping. The pressure relief
valves protect the refrigerant circuit against excessively
high pressures.
The pressure relief valve on the low-pressure side opens
when an excessively high pressure occurs in the refrigerant
circuit when the system is switched off. This can occur if the
refrigerant is heated in warm ambient conditions, causing
the system pressure to increase. The pressure control valve
opens at a pressure of about 1740.4 psi ± 145 psi (120 bar
± 10 bar)

In this case, the pressure control valve opens at a pressure
of about 2320.6 psi ± 145 psi (160 bar ± 10 bar).
Two valves have different diameters to prevent from being
installed in the wrong locations. Both valves have a lefthanded thread.
A valve with an M12x1 thread is used on the high-pressure
side and a valve with an M14x1 thread on the low-pressure
side. The valves have different tightening torques.
The pressure relief valve on the low-pressure side is located
at the block connection from the internal heat exchanger.
The pressure relief valve on the high-pressure side is
located directly at the AC compressor.

The pressure relief valve on the high-pressure side opens if
an excessively high system pressure occurs due to a fault in
the control system or a damaged or clogged line on the
high-pressure side.

Note
If the valve has opened, it will be indicated by a broken protective foil. An opened valve must be replaced. The refrigerant
must be evacuated completely before removing the valves.

9

Expansion valve
The expansion valve is the interface between the high and
low-pressure sides.
The task of this valve is to expand and cool the highly
pressurized refrigerant at a low pressure level.

It acts as a high-pressure-controlled expansion element for
the evaporator. The refrigerant is expanded at medium and
high load using a defined bore diameter of 0.55 mm. At
high load, an additional bypass flow is opened in a controlled manner by a spring.

Adjusting spring

Metallic gasket
Refrigerant (high pressure / atmosphere)

Filter

Metal bellows

Closing element with
0.55 mm bore diameter

Bypass seat with defined
bore diameter

Aluminum housing

665_007

Evaporator
The task of the evaporator is to extract heat the passenger
compartment.
The evaporator consists of flat tubes, in each of which
small tubes are bundled longitudinally. The refrigerant is
circulated several times through these tubes. They are
arranged in two vertical rows (one behind the other) inside
the evaporator. The key here is that the refrigerant mass
flow is distributed evenly to all flat tubes.

10

Accumulator
The accumulator is integrated into the refrigerant circuit on
the low-pressure side between the evaporator and the
internal heat exchanger. It has a diameter of about 2.95 in
(75 mm) and is built into the wheel well on the driver's side
under the A pillar.
The accumulator has the following tasks:
›› Header / reservoir for non-circulating refrigerant.
›› Reservoir for refrigerant oil.
›› Drying and extracting water from the circulating
refrigerant.

Inlet

The accumulator ensures that the refrigerant is of the
optimal quality, that is, having the ideal vapor content for
the internal heat exchanger.
After the refrigerant enters the accumulator it comes into
contact with the baffle plate, where the liquid phase is
separated from the gaseous phase. Excess refrigerant is
stored in the header after it has been filtered and dried. The
refrigerant oil is also filtered and flows through a bore in
the intake manifold into the refrigerant circuit leading to
the AC compressor together with the refrigerant emerging
from the accumulator.

Outlet

Baffle plate

Filter

Header
Granulate

Bore

Oil filter

665_008

11

Refrigerant lines
Refrigerant lines on hot gas side

Refrigerant lines on high and
low-pressure sides

The refrigerant on the hot gas side is a hose and pipe
connection from the compressor to the gas cooler.

The refrigerant lines on the high and low-pressure sides are
hose or tube connections without a corrugated tube reinforcement.

Corrugated tube reinforcement

665_024

665_025

The high temperatures of the compressed refrigerant necessitate channeling it through a corrugated metallic pipe held in
shape by a steel-fiber reinforced tubing.

Working pressure in the refrigerant lines
›› The working pressure is approximately 2030.5 psi (140 bar).
›› The refrigerant lines are designed for temperatures from
approximately -40 °F to 356 °F (-40 °C to 180 °C).

Note
If repairs are needed, the complete refrigerant system must always be checked for an absence of pressure. There should be
absolutely no pressure in the system. Close attention must be paid to cleanliness. The connections must be perfect before
tightening. The refrigerant lines must not be flexed and the refrigerant hoses must not be kinked during the tightening,
removal or re-installation procedures.

12

Connection system
The refrigerant lines have special gaskets which are
designed to withstand the high pressures within the
refrigerant circuit and to seal it against the atmosphere.
The actual metal gasket is located inside the locking device
(yellow element). The refrigerant lines are interlocked with
the locking device by a pin.

The locking device, including the gasket as well as the
retaining bolt, must be replaced whenever the refrigerant
lines are repaired. This is necessary in order to ensure the
maximum integrity of the refrigerant system. When carrying out this work, pay close attention to cleanliness and
make sure that the gasket is properly seated during
installation.
It is also important to make sure that the sealing faces are
oil and grease free before installing the refrigerant lines.

Refrigerant line

Metallic gasket

Locking device

Pin

Retaining bolt

665_013

Note
The metallic gasket can only seal the system if the retaining bolt is tightened to the correct specified torque value.

13

Refrigerant pressure and temperature sensors G1052 / G1053
The refrigerant pressure and temperature sensors G1052
and G1053 have different tasks and installation positions.
The tasks for Low Pressure Side A/C Pressure/Temperature
Sensor G1052 are to supply signals for low pressure control
and low fill level detection. It is attached to the low pressure line on the output side of the accumulator.
The tasks for High Pressure Side A/C Pressure/Temperature
Sensor G1053 are to supply signals for high pressure and
hot gas temperature control, in order to protect the components of the compressor. It is attached to the high pressure line directly at the inlet side of the gas cooler.

The refrigerant pressure and temperature sensors G1052
and G1053 are only installed in systems equipped with a
CO₂ climate control. The reason for this is that CO₂ climate
control systems operate at high pressures. If either or both
of these sensors needs to be replace due to repair work, the
complete refrigerant circuit must be evacuated. The two
sensors must never be loosened when system is active and
under high pressure because they are integrated directly in
the refrigerant circuit.
G1052 and G1053, have neither a safeguard nor a pressure
relief valve.

Low Pressure Side A/C Pressure/Temperature Sensor
G1052

High Pressure Side A/C Pressure/Temperature Sensor
G1053

665_009

14

Vehicle Interior Carbon Dioxide Concentration Sensor G929
(for European vehicles only)
G929 is located in the passenger compartment under the glove compartment. The working principle of the sensor is based
on measuring the wavelength-dependent radiation characteristics of carbon dioxide (CO₂).

665_012

The task of Vehicle Interior Carbon Dioxide Concentration
Sensor:

The following steps are taken if excessively high CO₂
levels are detected:

›› Measurement of cabin CO₂ concentration in driving mode
and when parking.

›› The ambient air supply is increased by opening the
ambient air flap / air recirculation flap in order to reduce
CO₂ concentration levels. If the CO₂ concentration level
continues to rise, the speed of the cabin fan is increased
to the maximum level.

Intervention points:
›› The intervention point varies depending on operating
state.
›› At low CO₂ concentration levels during normal operation.
›› At elevated CO₂ concentration levels in air recirculation
mode.
›› At high CO₂ concentration levels in the parked vehicle.

›› If the concentration level rises still further, the driver
information system in the instrument cluster issues the
following warning: "Air conditioning system: high CO₂
concentration. Ventilate vehicle. See owner's manual“.
›› If high CO₂ values are detected inside the parked vehicle,
the fan is started by Vehicle Electrical System Control
Module 1 J519.

15

Components of the R744 refrigerant circuit
The illustration provides a location overview of the components
described on the previous pages.

Service connection,
low-pressure side

Connection to evaporator

Gas cooler

System pressure
›› The system pressure on the low-pressure side is about
1348.8 psi (93 bar).
›› The system pressure on the high-pressure side is about
2030.5 psi (140 bar).

16

High Pressure Side A/C
Pressure/Temperature
Sensor
G1053

AC compressor with
pressure relief valve,
high-pressure side

Service connection,
high-pressure side

Expansion valve

Low Pressure Side A/C Pressure/
Temperature Sensor G1052

Accumulator

Internal
heat exchanger

Pressure relief valve,
low-pressure side

665_011

17

Topology

Data Link Connector

Data Bus on Board
Diagnostic Interface
J533

Front Information Display Control
Head
J685

Front Information Display Control
Head 2
J1060

Information
Electronics Control
Module 1
J794

Air Quality Sensor
G238

Left Rear Air Distribution Motor
V593

Left Footwell Door
Motor
V108

Left Rear Air Door
Motor
V239

Exterior Air Quality
and Humidity Sensor
G935

Humidity Sensor in
Fresh Air Intake
Duct
G657

Left Footwell Vent
Temperature Sensor
G261

Right Footwell Vent
Temperature Sensor
G262

Evaporator Vent
Temperature Sensor
G263

Vehicle Electrical System Control Module 1
J519

A/C Compressor with
Magnetic Clutch and
Regulator Valve
VX81

Speed Sensor 4
G656

A/C Compressor
Regulator Valve
N280

Rear Sunlight Photo
Sensor
G914

Air Ionization
System Control
Module
J897

Driver Side Ionizer
J1105

Front A/C Display
Control Head 1
E774

Front A/C Display
Control Head 2
E775

Front Passenger
Side Ionizer
J1106

Right Rear Upper
Body Vent Motor
V316

Right B-Pillar/Footwell Shut-Off Door
Motor
V211

Center Air Vent
Cover Motor
V208

Right Air Vent Cover
Motor
V209

Right Side Window
Defroster Door
Motor
V410

A/C Clutch
N25

Low Pressure Side A/C Pressure/Temperature
Sensor
G1052

Air Freshening System Control Module
J1101

High Pressure Side A/C Pressure/Temperature
Sensor
G1053

Fragrance Diffuser
System Blower
V686

18

Vehicle Interior Carbon Dioxide Concentration Sensor
G929

Left Side Window
Defroster Door
Motor
V409

Left Air Vent Cover
Motor
V207

Fragrance System
Functional Unit
GX43

Fresh Air Blower
Control Module
J126

Fresh Air Blower
V2

Fragrance Diffuser
System
Temperature Sensor
G1056

Auxiliary Heater
Control Module
J604

Auxiliary Heater
Heating Element
Z35

Fragrance Diffuser
System Actuator
V687

Fresh Air Door
Motor
V438

Recirculation Door
Motor
V113

Auxiliary Display
Control Head 1
E857

Wireless Control
Head 1
E859

Right Rear Air Door
Motor
V240

Right Center Vent
Motor
V111

Defroster Door
Motor
V107

Left Side Vent
Motor
V299

Left Temperature
Control Door
Motor
V158

Left Center Vent
Motor
V110

Right Temperature
Control Door
Motor
V159

Right Rear Air
Distribution
Motor
V594

Right Footwell
Door Motorr
V109

Right Side Vent
Motor
V300

Right Rear Heated
Seat Temperature
Sensor
G95

Right Rear Seat
Backrest Temperature Sensor
G809

Left Front Upper
Body Vent Temperature Sensor
G385

Right Front Upper
Body Vent Temperature Sensor
G386

Position Sensor in
Left Center Vent
G626

Position Sensor in