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Removing and installing heat exchanger of air conditioning unit > < Removing and installing supplementary air heater elementZ35 / honeycomb element

A4 Mk3

Checking electric supplementary heater
Checking electric supplementary heater
  Note
t  Vehicles with a diesel engine and vehicles with certain petrol engines (e.g. petrol engines designed for operation with bioethanol installed in „Flex Fuel Vehicle“ as of Model Year 2010 and vehicles with a high-voltage system) are currently fitted with an electric supplementary heater as supplementary air heater → Audi Sales Range. Heat energy is supplied to the air after leaving the heat exchanger of the air conditioning unit in the event of a request from the air conditioner operating and display unit, Climatronic control unit -J255-.
t  Heat energy is added to the air after leaving the heat exchanger of the air conditioning unit by way of the supplementary air heater element -Z35-. At a later date (introduction not yet finalised), it will also be possible to actuate an auxiliary heater (fitted as an optional extra) as a „supplementary heater“ → Chapter and → Auxiliary heater; Rep. gr.82.
t  Vehicles not fitted with a supplementary air heater element -Z35- are provided instead of -Z35- with a honeycomb element in the air conditioning unit → Chapter.
t  The electric supplementary heater (supplementary air heater element -Z35-) is actuated on vehicles with a diesel engine by way of the corresponding engine control unit (the control units exchange the appropriate information by way of the data bus) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Current flow diagrams, Electrical fault finding and Fitting locations.
t  On vehicles with a petrol engine, the electric supplementary heating (supplementary air heater element -Z35-) is actuated by a signal from the operating and display unit, Climatronic control unit -J255- by way of the local data bus (via the same output by which the fresh air blower control unit -J126- is actuated) to the supplementary air heater control unit -J604-. -J604- then actuates the low heat output relay -J359- and the high heat output relay -J360- (and these supply power to -Z35-) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Current flow diagrams, Electrical fault finding and Fitting locations.
t  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 / supplementary air heater control unit -J604- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. On vehicles with a diesel engine, the measured value block of the engine control unit then indicates implementation of the request or the reason for non-actuation despite the request → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  The supplementary air heater control unit -J604- fitted on vehicles with certain petrol engines has no diagnosis capability at present → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  Vehicles with a high-voltage system (hybrid vehicles) and petrol engine are currently also fitted with a supplementary air heater element -Z35- → Chapter.
t  Checking actuation of the supplementary 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 this vehicle. For vehicles with a petrol engine, this can be found in the guided fault-finding for the air conditioner → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  In Model Year 2009, a modified version of the supplementary air heater element -Z35- (slightly slimmer heating element design) was gradually introduced. Pay attention the correct version and assignment → Electronic parts catalogue.
t  As of Model Year 2010 a start/stop system will be available as an optional extra for this vehicle in conjunction with certain engines. On vehicles with a start/stop system, the supplementary air heater element -Z35- is deactivated whilst the stop function is active (to protect the battery -A-). Once the engine has been re-started via the start function, the supplementary air heater element -Z35- is actuated again → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  For checking the resistance value of the supplementary air heater element -Z35-, refer to → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
Design and operation of the supplementary air heater element -Z35-
   
t  The supplementary air heater element -Z35- is made up of several layers of resistor elements -E- and -F-. Given simultaneous actuation via all 3 inputs -A- to -C-, these can attain a joint heat output of approx. 1000 W. These resistor elements have a positive temperature coefficient (the resistance increases with temperature and the current input and thus the heat output decrease).
t  The resistor-type heater elements (-E- and -F-) are actuated by way of the wires -A- to -C-. The current is discharged via the earth connection -D-.
t  The design of the supplementary air heater element -Z35- is such that a current greater than 35 A cannot flow via any of the contacts -A- to -C- on switch-on. Immediately after switch-on, the resistance of the resistor-type heater elements -E- and -F- increases and the current decreases.
t  To attain the maximum heat output of approx. 1000 W (3 x 333 W), the temperature of the resistor-type heater elements must be low and sufficient current must be supplied by the alternator -C-.
t  Voltage is switched by way of the low heat output relay -J359- via the wire -A- to the resistor-type heater elements -F- → Current flow diagrams, Electrical fault finding and Fitting locations.
t  Voltage is switched by way of the high heat output relay -J360- via the wires -B- and -C- to the resistor-type heater elements -E- → Current flow diagrams, Electrical fault finding and Fitting locations.
t  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 the connector) and the earth connection -D-.
  Note
t  For measuring the resistances and checking actuation of the supplementary air heater element -Z35-, unplug the connector at the air conditioning unit → Chapter.
t  As resistances of less than 10 ohms cannot be measured with sufficient accuracy using workshop equipment, it is not possible to establish a short circuit in the supplementary air heater element -Z35-.
t  To check operation, actuate the low heat output relay -J359- and the high heat output relay -J360- e.g. by way of the „final control diagnosis“ function of the corresponding engine control unit and in doing so measure the voltage between the contacts in the mating plug to the connector at the supplementary air heater element -Z35- and earth → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  The engine control unit / supplementary air heater control unit -J604- actuate the supplementary air heater element -Z35- in 3 stages. Fot this purpose, contacts -A-, -B- and -C- are supplied with voltage as follows. The corresponding wiring can be seen from the appropriate 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 switched via the high heat output relay -J360- to contacts -B- and -C-.
–  For stage „3“, stage „1“ is switched in in addition to stage „2“. → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
  Note
The corresponding engine control unit constantly monitors the capacity utilisation of the alternator -C-. If this remains below a certain limit, the next stage is switched in. Switching back a stage is effected if a specified limit is exceeded.
Cut-in criteria for actuation 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 prerequisites must be met for the air conditioner operating and display unit, Climatronic control unit -J255- to transmit a request for supplementary heater activation to the engine control unit:
t  Engine running for at least 8 seconds and engine speed higher than 500 rpm.
t  Engine temperature less than 75 °C
t  Calculated ambient temperature less than 8 °C.
t  Electrical system voltage greater than 12.2 V and onboard supply control unit -J519- not transmitting any request preventing activation.
t  No faults stored in air conditioner operating and display unit, Climatronic control unit -J255-
t  No faults stored in engine control unit and capacity utilisation of alternator -C- less than 30 ...77 % (depending on engine speed)
t  On the basis of the setting and the temperatures measured, the air conditioner operating and display unit, Climatronic control unit -J255- has calculated that additional heat output is required to attain the specified passenger compartment temperature
t  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 / supplementary air heater control unit -J604- uses the two supplementary heater relays (low heat output relay -J359- and high heat output relay -J360-) to actuate the supplementary air heater element -Z35- (3-stage) such that the capacity utilisation of the alternator -C- does not exceed 95 % → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (for engine control unit on vehicles with a diesel engine or 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 in if the capacity utilisation of the alternator -C- is less than 30 ...77 % depending on the engine speed.
Shut-off criteria for actuation of electric supplementary heater
  Note
Deactivation takes place as soon as a cut-in criterion is no longer satisfied 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 heater if:
t  One of the cut-in prerequisites is no longer satisfied.
t  The calculated ambient temperature is greater than 11 °C.
t  The capacity utilisation of the alternator -C- is greater than 95 %.
t  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).
  A87-10524

Removing and installing heat exchanger of air conditioning unit > < Removing and installing supplementary air heater elementZ35 / honeycomb element