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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.
