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Removing and installing heat exchanger of air conditioning unit (heater) > < Removing and installing left temperature flap control motorV158 / temperature flap control motorV68

A3 Mk2

Removing and installing supplementary air heater elementZ35 (with supplementary air heater control unitJ604)
Removing and installing supplementary air heater element -Z35- (with supplementary air heater control unit -J604-)
  Note
t  Vehicles with diesel engine are currently fitted with an electric supplementary air heater. With this system, heat energy is supplied to the air after leaving the heat exchanger of the heater or air conditioning unit in the event of a request from the operating and display unit, Climatronic control unit -J255- or from the air conditioning system control unit -J301-. The electric supplementary air heater is actuated by the supplementary air heater control unit -J604- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 or by the engine control unit (with the 3-stage version via the low heat output relay -J359- and the high heat output relay -J360-) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (guided fault-finding for the corresponding engine control unit) and → Current flow diagrams, Electrical fault finding and Fitting locations.
t  There are different versions of the electric supplementary air heater. On vehicles with diesel engine manufactured up to November 2006 (gradual conversion), the supplementary air heater element -Z35- is actuated by way of the supplementary air heater control unit -J604- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. Vehicles with diesel engine manufactured as of November 2006 (gradual conversion) are fitted with a 3-stage supplementary air heater element -Z35- which is actuated by the corresponding engine control unit via a relay → Current flow diagrams, Electrical fault finding and Fitting locations.
t  Vehicles with diesel engine and „auxiliary heater“ optional extra are currently also fitted with a supplementary air heater element -Z35-. At a later date (introduction not yet finalised), the supplementary air heater element -Z35- is to be discontinued on these vehicles. The „auxiliary heater“ will then assume the function of the „supplementary heater“ → Auxiliary heater; Rep. gr.82.
t  Checking the actuation function of the electric supplementary air heater for a vehicle with supplementary air heater control unit -J604- is described in the air conditioner guided fault-finding → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  The measured value block of the supplementary air heater control unit -J604- shows that the supplementary heater is being actuated or indicates why there is no actuation in spite of a corresponding request → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  Checking actuation of the electric supplementary air heater for a vehicle with a 3-stage supplementary air heater element -Z35- is described in the guided fault-finding for the corresponding engine control unit → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  Vehicles with petrol engine are currently not fitted with a supplementary heater. The auxiliary heater is also not actuated as supplementary heater. → Auxiliary heater; Rep. gr.82
t  All replacement air distribution housings have an opening to accommodate a supplementary heater element. On vehicles with no supplementary air heater element -Z35-, the opening is sealed off by the heat exchanger cover (different versions). → Electronic parts catalogue
Removing
–  Remove the driver's storage compartment. → General body repairs, interior; Rep. gr.68
–  Remove the centre console. → General body repairs, interior; Rep. gr.68
   
–  Remove the left footwell vent -A- (driver side). → General body repairs, interior; Rep. gr.68
–  Remove the holder -B- → General body repairs, interior; Rep. gr.68.
  A87-0684
–  Remove the 4 bolts -A- and detach the cover -B-.
  Note
t  There are different versions of the cover -B- (for vehicles without or with electric supplementary heater) → Electronic parts catalogue.
  A87-0685
t  If the lever to the left temperature flap is positioned such that the upper bolt -A- is not accessible, switch on the ignition and select a different temperature setting (on the operating and display unit, Climatronic control unit -J255- for the left side, e.g. setting „Hi“).
Further procedure for vehicles with supplementary air heater control unit -J604-
–  Switch off ignition.
–  Interrupt the power supply to the supplementary air heater element -Z35- by removing the corresponding fuse (currently 100 A). The fuse fitting location is indicated in the relevant current flow diagram → Current flow diagrams, Electrical fault finding and Fitting locations
  A87-0685
–  Unplug the connector -A- from the heater element -D-.
–  Using a voltage tester, for example, check that there is no longer any voltage between the connections -C- (positive) and -B- (negative) (danger of short circuit).
–  Mark the two wires to the supplementary air heater element -Z35- (danger of interchange, vehicles with supplementary air heater control unit -J604- only).
  Note
If the connection assignment is interchanged, the supplementary air heater control unit -J604- can no longer regulate the current and there is a constant flow of current through the supplementary air heater element -Z35- (with maximum heat output and no regulation).
–  Detach both wires -B- and -C- to the supplementary air heater element -Z35- (tightening torque of hexagon nuts 6 Nm) and insulate the connection points (danger of short circuit).
  A87-0708
–  Pull the supplementary air heater element -Z35--A- (together with the supplementary air heater control unit -J604--B-, cannot be checked and replaced separately) out of the air conditioning unit (heater).
Further procedure for vehicles with 3-stage supplementary air heater element -Z35- (with no supplementary air heater control unit -J604-)
–  Switch off ignition.
  A87-0709
–  Remove the hexagon nut -A- (tightening torque 6 Nm).
–  Unplug the connector -B- from the supplementary air heater element -Z35--C-.
–  Pull the supplementary air heater element -Z35--B- out of the air conditioning unit (heater).
Installing
Then re-install all components removed in reverse order.
  Note
  A87-10280
t  The hexagon nuts at the two wiring connections -B- and -C- to the supplementary air heater element -Z35- are tightened to 6 Nm (excessive torque would damage the electronics of the supplementary air heater element -Z35-).
  A87-0709
t  The hexagon nut -A- at the connector -B- and the earth connection of the supplementary air heater element -Z35--C- is tightened to 6 Nm. Excessive torque could damage the electrics of the supplementary air heater element -Z35-.
–  If applicable, check actuation and operation of the supplementary air heater element -Z35- after installation → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (vehicles with air conditioner) and → Chapter (vehicles with no air conditioner).
  A87-10280

Removing and installing heat exchanger of air conditioning unit (heater) > < Removing and installing left temperature flap control motorV158 / temperature flap control motorV68