Checking activation of supplementary heater (auxiliary air heater element Z35) — AUDI

Checking activation of supplementary heater (
auxiliary air heater element
Z35
)
Components involved in activation of supplementary heater:
Heat energy is added to the air after it leaves the heat exchanger for the heater via the
auxiliary air heater element
Z35
Vehicle diagnostic tester
(
“Guided Fault Finding”
). This is only the case if there is a request from the operating unit (
heater control unit
J65
on vehicles without air conditioner /
air conditioning system control unit
J301
on vehicles with manually controlled air conditioner /
Climatronic control unit
J255
on vehicles with automatically controlled air conditioner).
Note
To protect the
battery
A
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.
Z35
is activated again as soon as the engine has been re-started via the start function
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
Vehicles with high-voltage system are currently not fitted with an
auxiliary air heater element
Z35
; on these vehicles, the
high-voltage heater (PTC)
Z115
(with
high-voltage heater (PTC) control unit
J848
) assumes the function of the auxiliary air heater element
Chapter
“
Notes on
high-voltage heater (PTC)
Z115
(and
high-voltage heater (PTC) control unit
J848
)
”
.
Cut-in criteria for activation of supplementary heater
Z35
The cut-in criteria must be met in the operating unit (
J65
,
J301
or
J255
) and in the engine control unit.
The following conditions must be met for the operating unit (
J65
,
J301
or
J255
) to transmit a request for the activation of the supplementary heater to the engine control unit:
“Automatic supplementary heating”
function not deactivated (on radio or MMI display)
Owner's Manual
Engine running for at least 8 seconds and engine speed above 500 rpm
Engine temperature below 75 °C
Calculated ambient temperature below 6 ℃
Stop function of start/stop system not active
Electrical system voltage above 12.2 V and
onboard supply control unit
J519
not transmitting any request preventing activation
No fault stored in operating unit (
J65
,
J301
or
J255
)
No faults stored in engine control unit, and load of alternator
C
less than 30 ... 77 % (depending on version of engine control unit)
Vehicle diagnostic tester
(
“Guided Fault Finding”
)
Due to the setting and the measured temperatures, the operating unit (
J65
,
J301
or
J255
) has calculated that additional heating output is required to reach the temperature specified for the passenger compartment.
More than 90 % of the air (position of temperature flaps) is being routed through the heat exchanger for the left or right side.
Note
The engine control unit activates the
auxiliary air heater element
Z35
via the
low heat output relay
J359
and the
high heat output relay
J360
so that the load of the alternator
C
does not exceed 95 %. The next stage is only switched on if the load of the alternator is below 30 ... 77 %, depending on the engine speed
Vehicle diagnostic tester
(
“Guided Fault Finding”
) and
Current flow diagrams, Electrical fault finding and Fitting locations
.
Shut-off criteria for activation of supplementary heater
Note
Activation is switched off as soon as the
“Automatic supplementary heating”
function is deactivated (on radio or MMI display), a cut-in criterion in the operating unit (
J65
,
J301
or
J255
) or in the engine control unit is no longer met or one of the shut-off criteria is detected.
The operating unit (
J65
,
J301
or
J255
) deactivates the request for activation of the electric supplementary heater under the following conditions:
One of the cut-in criteria is no longer met.
The calculated ambient temperature is above approx. 8 ℃.
The load of the alternator
C
is above 95 %.
Less than 60 % of the air is being routed through the heat exchanger for the left and right side (position of temperature flaps).
Stop function of start/stop system active