Electrical Auxiliary Heater, Testing
For these vehicles (For example the Audi A4) there are different versions of the heating and A/C system depending on the equipment. Make sure to use the correct version and pay attention to the allocation of different components. Refer to HEATING AND A/C SYSTEM VERSIONS .
On vehicles with a diesel engine without the "parking heater" optional equipment currently an auxiliary heater is installed. Heat energy is added to air on this system after it has left the heater and A/C unit heater core unit if there is a request from the Front A/C Display Control Head -E87-.
For specific vehicles with a gasoline engine depending on the version and the market in the future an Auxiliary Heater Heating Element -Z35- can also be installed (introduction not yet finalized). Refer to the appropriate Wiring Diagram(s).
For vehicles with a diesel engine and the optional "parking heater", installation of the electric auxiliary heater depends on the version of the vehicle. If no electric auxiliary heater is installed the parking heater takes the task of the electric auxiliary heater. Refer to GENERAL INFORMATION [R134a] / GENERAL, TECHNICAL DATA [R1234yf] and the Audi Sales Program.
The electrical auxiliary heater is activated by the Engine Control Module -J623- via the Low Heat Output Relay -J359- and the High Heat Output Relay -J360-. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the respective engine control module). Refer to the appropriate Wiring Diagram(s).
In the "read measured values" function of the Guided Fault Finding of the Front A/C Display Control Head -E87- is displayed that the request to activate the electrical auxiliary heater is being sent to the Engine Control Module -J623-. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
The check of the activation of the Auxiliary Heater Heating Element -Z35- via the Engine Control Module -J623- is located in the Guided Fault Finding. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
A start-stop system is available for this vehicle. For vehicles with a start-stop system, the Auxiliary Heater Heating Element -Z35- activation is switched off for the time in which the stop function is active (to protect the Battery -A-). After the motor was started again via the start function, the Auxiliary Heater Heating Element -Z35- is activated again. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
Switch-On Criteria for Auxiliary Heater Activation
Certain heating and A/C system functions (for example auxiliary heater activation) can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car" / "vehicle" menu. The A/C system control can also be influenced via the presets in the MMI (Multi Media Interface) under the "A/C system" function in the "Car" / "Vehicle" menu. Therefore, check the preset in the MMI first in the case there is a concern with these components. Refer to Infotainment/MMI Owner's Manual.
The following switch-on conditions must be met in the Front A/C Display Control Head -E87- and the respective engine control module.
Only installed on vehicles with a diesel engine at this time
-- The Front A/C Display Control Head -E87- sends a request to switch on the auxiliary heater to the engine control module as long as the following requirements are fulfilled:
- Engine is running for a minimum of 8 seconds and engine speed is greater than 500 RPM.
- Engine temperature is lower than 75 °C (167 °F).
- The calculated outside air temperature is lower than 8 °C (46.4 °F).
- The stop function for the Start/Stop System is not active.
- The electrical system voltage is greater than 12.2 volts and no request that forbids the switch-on is sent by Vehicle Electrical System Control Module -J519-.
- No malfunction is stored in the Front A/C Display Control Head -E87-.
- No malfunction is stored in the engine control module and the Generator -C- load is less than 30 to 77% (depending on the engine speed, this does not apply to activation of the fuel-driven parking heater as the auxiliary heater).
- On the basis of the setting and the measured temperatures, the Front A/C Display Control Head -E87- calculated that additional heat output is necessary to achieve the intended passenger compartment temperature.
- More than 90% of the air (position of temperature doors) is directed through the heater core for the left or right side.
The engine control module activates the Auxiliary Heater Heating Element -Z35- via the Low Heat Output Relay -J359- and the High Heat Output Relay -J360- so that the Generator -C- load does not exceed 95% (the next level is only switched to in the event that the generator load is less than 30 to 77%, depending on the engine speed). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function. Refer to the appropriate Wiring Diagram(s).
Switch-Off Criteria for Auxiliary Heater Activation
The activation is switched off as soon as a switch-on condition in the Front A/C Display Control Head -E87- and in the respective engine control module is no longer met or if one of the switch off criteria is recognized.
-- The Front A/C Display Control Head -E87- switches off the request to activate the electrical auxiliary heater.
- When one of the switch-on requirements is no longer met.
- The calculated outside air temperature is higher than 11 °C (51.8 °F).
- The Generator -C- load is greater than 95%.
- Less than 60% of the air is directed through the heater core for the left and right sides (position of temperature doors).
- The stop function for the Start/Stop System is active.
The engine control module activates the Auxiliary Heater Heating Element -Z35- via the Low Heat Output Relay -J359- and the High Heat Output Relay -J360- so that the Generator -C- load does not exceed 95% (if the generator load exceeds 95%, the auxiliary heater heating element output is reduced in stages by approximately one third). Use the Vehicle Diagnostic Tester in"Guided Fault Finding" function. Refer to the appropriate Wiring Diagram(s).
Overview and function of the Auxiliary Heater Heating Element -Z35-
- The Auxiliary Heater Heating Element -Z35- is comprised of several layers of resistance elements -E and F-. These can achieve a heating output of approximately 1000 W via all three inputs -A through C-. These resistance elements have a positive temperature coefficient (the resistance increases with the temperature and the current draw and the heating output decrease).
- The resistance heating elements (-E- and -F-) are activated via the contact -A, B and C- ; the current flows through the ground connection -D-.
- The Auxiliary Heater Heating Element -Z35- is designed so that a current greater than 35 A can flow via the contacts -A through C- when switched on. Immediately after switching on, the resistance on the resistance heating elements -E and F- increases and the current goes down.
- To reach the maximum heating output of approximately 1000 W (3 x 333 W), the resistance heating elements temperature must be low and the Generator -C- must deliver enough current.
- Via the Low Heat Output Relay -J359- the tension switches via a wire to the contact -A- and from there to the resistance heating element -F-. Refer to the appropriate Wiring Diagram(s).
- Via the High Heat Output Relay -J360- the voltage is switched via the contacts -B and C- from there to the resistance heating element -E-. Refer to the appropriate Wiring Diagram(s).
- The resistance of the heating elements depends on the temperature; the resistance is approximately 0.2 to 5 Ω; measured between the contacts -A, B or C- and the ground connection -D-.
- The current is routed from the positive connections -A, B and C- to the ground connection -D- via the resistance elements -E and F- and the adjacent conductor rails and finned heat sink -G-.
- Via the finned heat sink -G-, the current is routed to conductor rails -E and F- and also the electrical energy converted into heat energy by resistance elements -E and F- is released to the air flowing by.
To measure the resistances and to check the activation of the Auxiliary Heater Heating Element -Z35-, disconnect the connector from the heater and A/C unit to the Auxiliary Heater Heating Element -Z35-. Refer to AUXILIARY HEATER HEATING ELEMENT -Z35-, REMOVING AND INSTALLING .
Since resistances smaller than 10 Ω can no longer be measured with sufficient accuracy using workshop tools, a short circuit in the Auxiliary Heater Heating Element -Z35- cannot be determined.
Activate the Low Heat Output Relay -J359- and the High Heat Output Relay -J360- to check the function, for example, "output diagnostic test mode" function for the respective engine control module. When doing so, measure the voltage between the contacts in the connector to the Auxiliary Heater Heating Element -Z35- and the ground. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function and the appropriate Wiring Diagram(s).
- The engine control module activates the Auxiliary Heater Heating Element -Z35- in three steps. Contacts -A, B and C- are supplied with voltage as follows. Refer to the wiring diagram for the respective wiring. Refer to the appropriate Wiring Diagram(s).
-- For stage "1", the voltage from the Low Heat Output Relay -J359- is switched to the contact -A-
-- For stage "2", stage "1" is switched off and the voltage is switched to contacts -B and C- via the High Heat Output Relay -J360-.
-- For stage "3", stage "2" and stage "1" are switched on. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
The respective control module constantly monitors the Generator -C- load. The next stage is selected if the load remains under a certain limit. If the load exceeds a specified limit, then the stage is switched down.