heating AUDI A8 2003 D3 / 2.G Technical Features Manual

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Humidity sender G355
Heating/Air Conditioner
At low ambient temperatures, when the
windscreen is extremely cold, the top third is
particularly susceptible to fogging.
To cover this area, the humidity sender G355
is fitted in front of the base of the rear view
mirror.
The sender is designed to detect the
following:
– Humidity level
– Sender ambient temperature and
– Windscreen temperature
All three functions are combined in the
sender housing.
The humidity sender is intended for all
equipment versions.The sender data enable the air conditioning
system to detect potential misting of the
windscreen in good time.
Before water vapour from the air in the
passenger compartment can form on the
windows, the output of the air conditioner
compressor and the blower speed are
automatically increased and the defrost flap
is opened further. Dry air is then routed from
the open defrost vents to the windscreen and
side windows via the evaporator and heat
exchangers.
Measurement of humidity level and
corresponding temperature
Physical principles
Humidity measurement involves determining
the water vapour content of the passenger
compartment air. The capacity of air to
absorb water vapour is governed by the air
temperature. It is thus necessary to
determine not only the humidity level but also
the corresponding air temperature in the
measurement area.The warmer the air, the more water vapour it
can absorb. Water starts to condense if this
water-vapour enriched air cools down again.
This results in fine droplets forming on the
windscreen.
SSP282_104

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The buttons for the seat heating and
ventilation options are integrated into the
front and rear control and display units
(refer to Page 74). Climate-controlled seats with heating and
ventilation function
The Audi A8 ´03 can be fitted with front and
rear climate-controlled seats as optional
equipment. These seats offer a combination
of seat heating and seat ventilation and can
be regulated individually for each occupant.
Heating/Air Conditioner
The corresponding feedback LED lights after
pushbutton activation of seat heating/seat
ventilation. The selected seat heating/seat
ventilation stage can be called up in the
display segment of the Climatronic control
unit J255 and in the MMI (Multimedia
Interface) climate control menu. Once seat
heating/seat ventilation has been activated, it
remains active even after switching off the air
conditioner by means of the ON/OFF button.The use of seat ventilation leads to lower
occupant skin temperatures. Automatic
additional seat heating operation controlled
as a function of temperature cancels the
cooling effect and the air flow is warmed.
The ventilation function promotes pleasant
conditions in the occupant's back and seat
area and eliminates sweating more quickly.
Under normal circumstances, the seat
ventilation function is deactivated
automatically after approx. 30 minutes.
SSP282_107 Seat heating
button
Seat ventilation
button

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Comfort seat
The seat heating and seat ventilation
functions are not incorporated into
automatic climate control mode.
Seat climate control is achieved by way of
integrated fans in the seat cushion and
backrest. Air ducts in the seat padding convey
the air warmed by the seat heating to the
occupant through the fine perforations in the
leather.
SSP282_108
Air ducts
in seat padding
Fan in seat cushion
Seat cushion
carbon heating mats Backrest carbon
heating mats
Side bolster
carbon heating matFan in backrest

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J126 Fresh-air blower control unit
J255 Climatronic control unit
J528 Sunroof electronics control unit
J533 Data bus diagnostic interface
N175 Left heat regulation valve
N176 Right heat regulation valve
N280 Air conditioning system compressor
regulating valve
N340 Humidity sender heater
T16 16-pin connector
(diagnostic connection)
V2 Fresh-air blower
V42 Temperature sensor blower
V50 Coolant circulation pump
V68 Temperature flap control motor
V71 Air-flow flap control motor
V102 Central vent control motor
V107 Defroster flap control motor
V108 Left footwell flap control motor
V109 Right footwell flap control motor
V110 Left central vent control motor
V111 Right centre vent control motor
V113 Air-recirculation flap control motor
V199 Front right defroster/chest vent
shutoff flap control motor
V200 Front left defroster/chest vent
shutoff flap control motor
V220 Rear left vent warm/cold flap
control motor
V221 Rear right vent warm/cold flap
control motor
Z42 Rear left footwell heater element
Z43 Rear right footwell heater element
Z45 Front left heated seat
Z46 Front right heated seat
Block diagram for
front air conditioner
Key
C20 Solar cells
G56 Dash panel temperature sensor
G65 High-pressure sender
G89 Fresh-air intake duct temperature
sensor
G92 Temperature flap control motor
potentiometer
G107 Sunlight penetration photosensor
G113 Air-flow flap control motor
potentiometer
G135 Defrost flap control motor
potentiometer
G136 Left central vent control motor
potentiometer
G137 Right central vent control motor
potentiometer
G138 Central vent control motor
potentiometer
G139 Left footwell flap control motor
potentiometer
G140 Right footwell flap control motor
potentiometer
G143 Air recirculation flap control motor
potentiometer
G150 Left vent temperature sender
G151 Right vent temperature sender
G191 Centre vent temperature sender
G238 Air quality sensor
G263 Evaporator outflow temperature
sender
G317 Front right defroster/
chest vent shutoff flap
control motor potentiometer
G318 Front left defroster/
chest vent shutoff flap
control motor potentiometer
G344 Temperature sender for front left seat
G345 Temperature sender for front
right seat
G347 Centre left vent sensor
G348 Centre right vent sensor
G351 Rear left vent warm/cold
control motor potentiometer
G352 Rear right vent warm/cold
control motor potentiometer
G355 Humidity sender
Heating/Air Conditioner

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MMMMMMMMMMMMM
M
V50 N175 N176G238 G65 G107 G348 G347Z43 Z42
J126
V2Z45 G344 Z46
G345 3015
SS
15A5A
75
S
25A
75
S
25A
C20
S
20A
N340G355
J528J533
S
10A
30
G89
G150 G151 G263
V221
V111 V110 V220
V102 V68 V109 V108 V199 V200 V107 V71 V113J255 V42 G5658S
58S
G143G113 G135
G318G317G139
G140G92
G138G351G136
G137G35231
inout
2
31
4
G191
N280
M
T16
Colour code
= Input signal
= Output signal
= Positive supply
= Earth
= Convenience CAN High
= Convenience CAN Low
= LIN busAdditional signals
Climate control LIN bus for
– Heated windscreen
control unit J505
– Driver seat ventilation
control unit J672
– Front passenger seat ventilation
control unit J673
1Terminal 30/blower
Terminal 30/front seat heating
Input/rear roller blind switch E1492
3
4
SSP282_109

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Z12
E265
S
20A
30
G178
31
in out
G426 G427 V219
G349G350
M
V218
MJ533
S
15A
30
S
5A
15
G95
S
5A
3075
S
20A
S
5A
75
Z11 Z10V273G177G94
MM
V271
J674
J675
T16
Heating/Air Conditioner
Block diagram for
rear air conditioner

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Auxiliary heater/coolant additional heater
An auxiliary heater is available as an option
for all vehicle and engine versions. The
auxiliary heater with petrol engines and
additional heater with diesel engines are
integrated into the engine coolant circuit.
Vehicles with diesel engine are fitted with an
additional heater as standard. On diesel
engines with auxiliary heater, the activated
auxiliary heater is also used as engine
additional heater depending on temperature.
Heating/Air Conditioner
Design and operation are described in
SSP 240 – Audi A2 Technical Features.
Operation with cut-in by way of remote
control or timer
In the Audi A8 ´03, the auxiliary heater is
activated by the air conditioner. The heated
coolant is initially supplied to the passenger
compartment (primarily auxiliary heater
mode). On attaining pre-determined
temperature levels, engine pre-heating is
then switched in in line with a characteristic
curve.
Activation sequence:
1 A remote control or timer signal is
transmitted to the auxiliary heater control
unit.
2 The auxiliary heater then transmits a signal
via the CAN bus to the Climatronic control
unit J255.
3 The control unit then decides as a function
of desired temperature, ambient
temperature and passenger compartment
temperature whether auxiliary ventilation
or auxiliary heating is to be employed.
The setting of the auxiliary heater/
ventilation function is shown in the setup
menu in the MMI (Multimedia-Interface).The cut-in time is "programmed" by way of
the MMI system (Multimedia Interface) under
the menu item "timer status".
4.1 Auxiliary ventilation sequence
The energy management control unit
J644 interrogates the battery capacity
check function of the battery and energy
management system to determine
whether auxiliary ventilation can be
accepted. In the event of acceptance, the
fresh-air blower is actuated.

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4.2 Auxiliary heating sequence
The level of fuel in the tank is
interrogated. If the fuel tank is "empty",
the auxiliary heating function is not
permitted and the auxiliary heater symbol
in the dash panel insert goes out. "Empty"
roughly corresponds to the red display
zone. The energy management control
unit J644 checks whether there is
sufficient energy to accept auxiliary
heating. If this is the case, the auxiliary
heater is switched on in the various
operating modes depending on the
characteristic temperature curve and the
fresh-air blower is actuated.
If the auxiliary heating temperature
reaches a level of 30 °C, the fresh-air
blower is activated and the coolant
shutoff valve N279 pulsed in line with the
characteristic curve.
The auxiliary heater is switched off
automatically on completion of the operating
time transmitted by the MMI system to the
Climatronic control unit or it can be switched
off using the remote control OFF button.
Auxiliary heater circulation pump control
To speed up heating of the passenger
compartment and to achieve a better "heat
yield" in the air conditioner unit heat
exchanger, the circulation pump V55 and
coolant shutoff valve N279 are pulsed as a
function of water temperature and the
heating circuit flow rate is thus reduced.
An electric circulation pump is used for the
auxiliary heater. It is not possible to reduce
the supply voltage in the auxiliary heater
control unit and the circulation pump is thus
actuated at specific intervals to decrease its
output.
Additional control curve for "auxiliary heater"
and "additional heater"
When the engine is on, the auxiliary heater
and engine temperatures are constantly
compared. A switch to the large coolant
circuit is made as soon as the engine
temperature exceeds the auxiliary heater
temperature.
Activation of auxiliary heater circulation
pump with engine on
(pulsed operation of circulation pump)
In order to be able to ensure a sufficient flow
of water through the heat exchanger, the
auxiliary heater circulation pump must
additionally be switched on, as is the case for
instance with the 12-cylinder engine.If the engine is switched off again and not
all additional heater criteria (temperature,
time) are satisfied, the auxiliary heater
remains in operation for any residual
operating time before being deactivated.
This function can be encoded.

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Small coolant circuit with auxiliary heater
The small coolant circuit employed with
auxiliary heating is designed to ensure rapid
warming of the passenger compartment.
With the engine stopped, the coolant shutoff
valve N279 switches to the small heating
circuit until a defined temperature value has
been attained. The coolant exiting from the
heat exchangers via the pump/valve unit is
conveyed by the circulation pump V55 into
the auxiliary heater. After being warmed, the
coolant is pumped back into the heat
exchangers and initially heats the passenger
compartment.
Heating/Air Conditioner
SSP282_097
Design and operation are described in
SSP 267 – The 6.0 l W12 engine in the
Audi A8 - Part 1.
Coolant shutoff
valve N279
Circulation pump V55Auxiliary heater with
additional heater control unit J364
Non-return valve 2
Continued coolant
circulation pump V51 Tempera-
ture
senderPump/valve unit with
heating-system heat
exchangers Cap
Coolant
circulation
pump V50