Audi Workshop Service and Repair Manuals > A3 Mk2 > Heating, ventilation, air conditioning system | Heating and air conditioning | Heating | Operation of heater controls (air conditioner controls), removing and installing | Functions of heater controls (heater control unitJ65) | Actuation of supplementary heater (on vehicles with no air conditioner)

Removing and installing heater controls / air conditioner controls > < Actuation of engine control unit (on vehicles with petrol direct injection engine "FSI" and/or with engine with map-co

Actuation of supplementary heater (on vehicles with no air conditioner)

Vehicles with diesel engine only

Note

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 in the event of a request from the heater controls (heater control unit -J65-). 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.

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 → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (guided fault-finding for the relevant engine control unit) and → Current flow diagrams, Electrical fault finding and Fitting locations.

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.

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.

Checking the actuation function 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

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.

Checking actuation by heater controls (heater control unit -J65-)

Special tools and workshop equipment required

t	105-pin test box -V.A.G 1598/42-1- and test adapter for AC operating element - Touran -V.A.G 1598/47-

t	Vehicle diagnostic, testing and information system -VAS 5051 A- with multimeter leads -VAS 5051/7-

t	A switch is fitted in the heater control unit -J65-. This switch is actuated (closed) by way of the rotary temperature setting control -A- in the range between approx. 3 o'clock and the „warm“ stop position.

–

If the supplementary heater switch is closed, earth is switched with the ignition on by the electronics in the heater control unit -J65- via contact „7“ to the supplementary air heater control unit -J604-/to the corresponding engine control unit. The supplementary air heater control unit -J604-/engine control unit recognises that additional heat output is required and switches on the electric supplementary heater provided that the other cut-in criteria required for actuation are also satisfied.

t	Cut-in criteria for electric supplementary air heater (actuation of supplementary air heater element -Z35- by supplementary air heater control unit -J604- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.

t	Cut-in criteria for auxiliary heater as supplementary heater (in supplementary heater control unit -J364-) on vehicles with this optional extra → Auxiliary heater; Rep. gr.82

Cut-in criteria for electric supplementary air heater (actuation of supplementary air heater element -Z35- by corresponding engine control unit) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (guided fault-finding for the relevant engine control unit).

Note

For the corresponding engine control unit to actuate the 3-stage supplementary air heater element -Z35- by way of the low heat output relay -J359- and the high heat output relay -J360-, the same criteria must be satisfied in the engine control unit as in the air conditioning system control unit -J301- for vehicles with manually controlled air conditioner → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.

Cut-in criteria for actuation of electric supplementary air heater

–	By way of the low heat output relay -J359- and the high heat output relay -J360-, the engine control unit actuates the supplementary air heater element -Z35- if the following prerequisites are met:

t	Heater control unit -J65- applying earth signal to 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 engine control unit and capacity utilisation of alternator -C- less than 30 ...77 % (depending on engine speed)

Note

On vehicles with 3-stage supplementary air heater element -Z35-, the engine control unit actuates the two supplementary heating relays 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 the engine control unit) and → 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 supplementary heater

Note

On vehicles with no air conditioner, actuation is shut off as soon as one of the cut-in criteria is no longer satisfied in the engine control unit or one of the shut-off criteria is detected.

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	Heater control unit -J65- no longer applying earth signal to engine control unit

Heating, ventilation, air conditioning system
Heating and air conditioning / Heating
Operation of heater controls (air conditioner controls), removing and installing / nctions_of_heater_controls_(heater_control_unitj65)/">Functions of heater controls (heater control unitJ65)
Actuation of supplementary heater (on vehicles with no air conditioner)

Removing and installing heater controls / air conditioner controls > < Actuation of engine control unit (on vehicles with petrol direct injection engine "FSI" and/or with engine with map-co