Auxiliary Heater Element: Service and Repair
Auxiliary Heater Heating Element (Z35) with Control Module (J604)
An auxiliary heater is installed for vehicles with diesel engines.
• In vehicles with a diesel engine, an electrical auxiliary heater is currently installed. The air is supplied with heat energy after leaving the heater core of the A/C unit if there is a request from the front A/C display control head, the Climatronic control module (J255).
• An electrical auxiliary heater is also currently installed in vehicles with a diesel engine.
• The electrical auxiliary heater is activated via the Auxiliary air heater control module. The Climatronic control module control module and Auxiliary air heater control module) exchange the relevant information with one another via a local data bus. Check using the (Vehicle diagnostic tester) in the "Guided Fault Finding" function and.
• Check the function of the electrical auxiliary heater and the Auxiliary air heater control module.
• In vehicles with a gasoline engine and in vehicles with a diesel engine in which an auxiliary heater heating element (Z35) is not installed, an A/C unit without an opening for installing an auxiliary heater heating element is installed. Refer to => [ Components Inside Passenger Compartment ] Components Inside Passenger Compartment and Electronic Parts Catalog (ETKA).
Removing
- Move the right front seat (passenger side seat) as far back as possible.
- Switch off the ignition.
- Remove the right (passenger) footwell vent. Refer to => [ Right Footwell Vent ] Right Footwell Vent.
• A/C system malfunctions in the case of interchanged control motors and/or connectors, refer to => [ A/C Control Motor Block Diagram ] A/C Control Motor Block Diagram.
• The control motors and connectors are identical. If they are installed or connected incorrectly, the corresponding doors cannot be properly adapted and/or activated.
• Clearly label control motors and connectors prior to removal to prevent incorrect installation.
- Remove the air intake housing. Refer to => [ Air Intake Housing Of Front A/C Unit ] Air Intake Housing Of Front A/C Unit.
- Remove the right center vent motor (V111). Refer to => [ Right Center Vent Motor (V111) ] Right Center Vent Motor (V111).
• Risk of short circuit when disconnecting the voltage supply to the auxiliary heater heating element (Z35).
• Remove the fuse in the voltage supply to the auxiliary heater heating element (Z35).
- Interrupt the voltage supply to the auxiliary heater heating element by removing the relevant fuse (current 150 A).
• The fuse location can be found in the appropriate wiring diagram.
- Disconnect the connector - A - from the auxiliary air heater control module - D -.
- Again check between connections - C - (positive) and - B - (negative) using a voltage tester. There must no longer be any voltage present (danger of short circuit).
• To prevent the - C - (positive) and - B - (negative) connections from being switched, they have different diameters (M6 threads and M8 threads on the Auxiliary air heater control module).
• If connections (- C - and - B -) are interchanged, the Auxiliary air heater control module can no longer regulate the current so that current flows continuously through the auxiliary heater heating element (unregulated with maximum heat output).
- Remove both wire connections - B - and - C - to the Auxiliary air heater control module.
- Individually insulate both wire connections - B - and - C - after removal (risk of short circuit).
- Remove bolts - E -.
The auxiliary heater heating element may be hot.
• If the auxiliary heater heating element is activated prior to removal, do not touch the auxiliary heater heating element.
- Pull the Auxiliary air heater control module - A - (with the auxiliary heater heating element - B -, cannot be individually checked and replaced) from installation shaft - C - of the A/C unit.
Installing
Installation is carried out in the reverse order while noting the following:
- With the auxiliary heater heating element - B - removed, check installation shaft - C - of the A/C unit for contamination and remove any dirt.
- Via installation shaft - C - for the auxiliary heater heating element, check the separation between the left and right side in the A/C unit.
- Insert the auxiliary heater heating element - B - with the Auxiliary air heater control module - A - into installation shaft - C - of the A/C unit.
- Install the auxiliary heater heating element - B - only with rubber mountings - D - on pins - E - in mounts - F - of the A/C unit
- Install the screws - E -.
- Install both wire connections - B - and - C - to the Auxiliary air heater control module.
• Tightening specification of the hexagon nut (thread M8) on connection - B - 20 Nm
• Tightening specification of the hexagon nut (thread M6) on connection - C - 9 Nm
- Install the removed parts in the opposite order.
- Perform the basic setting and the output diagnostic test mode of the A/C system using the (Vehicle diagnostic tester) in the "Guided Fault Finding" function.
• In this vehicle, the control motors are equipped with electronics. During the basic setting, a new control motor learns its position on the A/C unit and can then be activated by the front A/C display control head, the Climatronic control module (currently all control motors are identical). Check using the (Vehicle diagnostic tester) in the "Guided Fault Finding" function.
• During the basic setting, the control motors are assigned and adapted corresponding to the switching sequence of the wiring. If this sequence does not conform with the specification, the control motors will adapt incorrectly and the door control will be wrong. Refer to => [ A/C Control Motor Block Diagram ] A/C Control Motor Block Diagram.
- Check the event memory of the Climatronic control module and erase any displayed malfunctions using the (Vehicle diagnostic tester) in the "Guided Fault Finding" function.
- After installation check the activation and function of the auxiliary heater heating element via the Auxiliary air heater control module as necessary using the (Vehicle diagnostic tester) in the "Guided Fault Finding" function.