Checking auxiliary air heater element Z35 — AUDI

Checking
auxiliary air heater element
Z35
Note
Vehicles with a diesel engine and vehicles with certain petrol engines (e.g. petrol engines designed for operation with bioethanol installed in
“Flex Fuel Vehicles”
from model year 2010 onwards and vehicles with a high-voltage system) are currently fitted with an electric supplementary heater as an auxiliary air heater
Audi sales literature
. Heat energy is supplied to the air after it has left the heat exchanger of the air conditioning unit if there is a request from the air conditioner operating and display unit (
Climatronic control unit
J255
).
Heat energy is added to the air via the
auxiliary air heater element
Z35
after the air emerges from the heat exchanger of the air conditioning unit. At a later date (introduction not yet finalised), it will also be possible to activate an auxiliary heater (installed as optional equipment) as a
“supplementary heater”
Chapter
and
Auxiliary/supplementary heater
Rep. gr.
82
Overview of fitting locations - auxiliary/supplementary heater; Overview of fitting locations - components not located in passenger compartment
.
Vehicles without an
auxiliary air heater element
Z35
are fitted with a honeycomb element in the air conditioning unit (instead of
Z35
)
Chapter
.
On vehicles with diesel engine, the electric supplementary heater (
auxiliary air heater element
Z35
) is activated via the relevant engine control unit (control units exchange relevant information via data bus)
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
and
Current flow diagrams, Electrical fault finding and Fitting locations
.
On vehicles with a petrol engine, the electric supplementary heater (
auxiliary air heater element
Z35
) is activated by a signal from the operating and display unit (
Climatronic control unit
J255
) via the local data bus (via the same output by which the
fresh air blower control unit
J126
is activated) to the
auxiliary air heater control unit
J604
.
J604
then activates the
low heat output relay
J359
and the
high heat output relay
J360
(and these supply power to
Z35
)
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
and
Current flow diagrams, Electrical fault finding and Fitting locations
.
The measured value block of the air conditioner operating and display unit (
Climatronic control unit
J255
) shows that the request for activation of the electric supplementary heater is being transmitted to the relevant engine control unit / to the
auxiliary air heater control unit
J604
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
. On vehicles with a diesel engine, the measured value block of the engine control unit then indicates the implementation of the request or the reason why it is not activated despite the request
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
Currently the
auxiliary air heater control unit
J604
fitted on vehicles with certain petrol engines has no diagnosis capability
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
Vehicles with a high-voltage system (hybrid vehicles) and petrol engine are currently equipped with an electrical
auxiliary air heater element
Z35
to provide a supplementary heating function
Chapter
.
Checking the activation of the
auxiliary air heater element
Z35
depends on the engine version. For vehicles with a diesel engine this can be found in the Guided Fault Finding for the engine fitted in the particular vehicle. For vehicles with a petrol engine, this can be found in the Guided Fault Finding for the air conditioner
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
In model year 2009, a modified version of the
auxiliary air heater element
Z35
with slightly smaller heating elements is gradually being introduced; observe the correct version and assignment
Electronic parts catalogue
.
From model year 2010 onwards, a start/stop system (optional equipment) is offered for this vehicle in combination with certain engines. On vehicles with a start/stop system, the activation of the
auxiliary air heater element
Z35
is switched off while the stop function is active (to protect the
battery
A
). After the engine has been switched on again via the start function, the
auxiliary air heater element
Z35
is activated again
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
For information on how to check the resistance value of the
auxiliary air heater element
Z35
, refer to
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
Design and operation of
auxiliary air heater element
Z35
The
auxiliary air heater element
Z35
is made up of several layers of resistor elements
E
and
F
. Given simultaneous activation via all 3 inputs
A
to
C
, these can attain a combined heat output of approx. 1000 W. These resistor elements have a positive temperature coefficient (the resistance increases with temperature so that the current draw and thus the heat output decrease).
The heater resistor elements (
E
and
F
) are activated via wires
A
to
C
. The current is discharged via earth connection
D
.
The
auxiliary air heater element
Z35
is designed so that, when it is activated, it is not possible for a current above 35 A to flow via any of the contacts
A
to
C
. The resistance of the heater resistor elements
E
and
F
increases immediately following activation, and the current decreases.
To reach the maximum heating output of approx. 1000 W (3 x 333 W), the temperature of the heater resistor elements must be low and sufficient current must be supplied by the
alternator
C
.
Voltage is switched by way of the
low heat output relay
J359
via wire
A
to the heater resistor elements
F
Current flow diagrams, Electrical fault finding and Fitting locations
.
Voltage is switched via
high heat output relay
J360
via wires
B
and
C
to heater resistor elements
E
Current flow diagrams, Electrical fault finding and Fitting locations
.
The resistance of the heater elements is governed by temperature and is between approx. 0.2 and 5 Ω (measured between connections
A
,
B
and
C
(in connector) and earth connection
D
).
Note
For measuring resistance values and checking activation of
auxiliary air heater element
Z35
, unplug connector at air conditioning unit
Chapter
.
As resistance values of below 10 Ω cannot be measured with sufficient accuracy using workshop equipment, it is not possible to detect a short circuit in the
auxiliary heater element
Z35
.
To check the operation, activate the
low heat output relay
J359
and the
high heat output relay
J360
e.g. via the
“final control diagnosis”
function of the corresponding engine control unit and, while doing so, measure the voltage between the contacts in the mating plug to the connector at the
auxiliary air heater element
Z35
and earth
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
The engine control unit /
auxiliary air heater control unit
J604
activates the
auxiliary air heater element
Z35
in 3 stages. Voltage is applied to the contacts
A
,
B
and
C
as follows. For the corresponding wiring, please refer to the relevant current flow diagram
Current flow diagrams, Electrical fault finding and Fitting locations
.
For stage
“1”
, voltage is switched by the
low heat output relay
J359
to contact
A
.
For stage
“2”
, stage
“1”
is deactivated and voltage is switched via
high heat output relay
J360
to contacts
B
and
C
.
For stage
“3”
, stage
“1”
is activated in addition to stage
“2”
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
Note
The corresponding engine control unit constantly monitors the load of the
alternator
C
; if it remains below a certain limit, the next stage is switched on. If a specified limit is exceeded, it switches back a stage.
Cut-in criteria for activation of electric supplementary heater
Note
These cut-in criteria in the air conditioner operating and display unit (
Climatronic control unit
J255
) must be satisfied for a request to be transmitted to the corresponding engine control unit.
The following conditions must be met for the air conditioner operating and display unit (
Climatronic control unit
J255
) to transmit a request for the activation of the supplementary heating system to the engine control unit:
Engine running for at least 8 seconds and engine speed above 500 rpm
Engine temperature below 75 °C
Calculated ambient temperature below 8 °C
Electrical system voltage above 12.2 V and
onboard supply control unit
J519
not transmitting any request preventing activation
No faults stored in air conditioner operating and display unit (
Climatronic control unit
J255
)
No faults stored in engine control unit and load of
alternator
C
below 30 ... 77 % (depending on engine speed)
Due to the setting and the temperatures measured, the air conditioner operating and display unit (
Climatronic control unit
J255
) has calculated that additional heating output is required to reach the temperature specified for the passenger compartment.
The air conditioner operating and display unit (
Climatronic control unit
J255
) has calculated that more than 90 % of the air is being routed through the heat exchanger of the air conditioning unit.
Note
The engine control unit /
auxiliary air heater control unit
J604
activates the 3-stage
auxiliary air heater element
Z35
via the two supplementary heater relays (
low heat output relay
J359
and
high heat output relay
J360
) so that the load of the
alternator
C
does not exceed 95 %
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
(for engine control unit on vehicles with a diesel engine / for air conditioner control unit on vehicles with a petrol engine) and current flow diagram
Current flow diagrams, Electrical fault finding and Fitting locations
. The next stage is only switched on if the load of the
alternator
C
is below 30 ... 77 %, depending on the engine speed.
Shut-off criteria for activation of electric supplementary heater
Note
The activation is shut off as soon as one of the cut-in criteria is no longer met in the air conditioner operating and display unit (
Climatronic control unit
J255
) or in the corresponding engine control unit, or if one of the shut-off criteria is detected.
The air conditioner operating and display unit (
Climatronic control unit
J255
) cancels the request for activation of the electric supplementary heating system if:
One of the cut-in criteria no longer met
Calculated ambient temperature above 11 °C
Load of
alternator
C
above 95 %
The air conditioner operating and display unit (
Climatronic control unit
J255
) has calculated that less than 60 % of the air is being routed through the heat exchanger of the air conditioning unit (position of temperature flaps).