| Checking actuation of heater controls with heater control unit -J65- |
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| A switch is fitted in the heater control unit -J65-. This switch is actuated (closed) by way of the rotary temperature setting switch -1- in the range between approx. 3 o'clock and
„Warm“ stop position. |
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| 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 corresponding engine control unit. The engine control unit detects that additional heat output is required and switches on the supplementary air heater element -Z35- by way of the low heat output relay -J359- and the high heat output relay -J360- if the other cut-in criteria required for actuation are also satisfied → Vehicle diagnostic tester,
„Guided fault-finding“ function, TDI engine. |
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| Cut-in criteria for electric supplementary air heater, actuation of supplementary air heater element -Z35- by engine control unit → Vehicle diagnostic tester,
„Guided fault-finding“ function, TDI engine. |
Note | Certain criteria must be satisfied in the engine control unit before the corresponding engine control unit actuates the 3-stage supplementary air heater element -Z35- by way of the low heat output relay -J359- and the high heat output relay -J360- → Vehicle diagnostic tester,
„Guided fault-finding“ function, TDI engine. |
| Cut-in criteria for actuation of electric auxiliary air heater |
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| 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: |
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| Heater control unit -J65- applying earth signal to engine control unit |
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| Engine running for at least 8 seconds and engine speed higher than 500 rpm. |
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| Engine temperature below 75 °C |
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| Calculated ambient temperature below 8 °C |
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| Electrical system voltage above 12.2 V and onboard supply control unit -J519- not transmitting any request preventing activation |
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| No entry stored in engine control unit and capacity utilisation of alternator -C- less than 70 % (depending on engine speed). |
Note | On vehicles with a 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 % → Vehicle diagnostic tester,
„Guided fault-finding“ function (for 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 heating system |
Note | On vehicles without air conditioner, actuation is shut off as soon as one of the cut-in criteria is no longer met in the engine control unit or one of the shut-off criteria is detected. |
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| One of the cut-in criteria no longer met |
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| The calculated ambient temperature is greater than 11 °C. |
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| Capacity utilisation of alternator -C- above 95 % |
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| Heater control unit -J65- no longer applying earth signal to engine control unit |
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