Electronic Auxiliary Air Heater Starting Conditions

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Switch-On Criteria for Electric Auxiliary Heater Activation

NOTE:

Certain A/C system functions (for example, auxiliary heater activation) can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car" / "car systems" menu. The A/C system control can also be influenced via presettings in the MMI (Multi Media Interface) under the "A/C system" function in the "car" / "car systems" menu. Therefore, first check the presetting in the MMI in the case of a problem with these components, refer to Infotainment/MMI Operating Instructions.

These switch on conditions in the Climatronic Control Module -J255- control head must be fulfilled, so that the request is sent to the respective engine control module/auxiliary heater.

The Climatronic Control Module -J255- must be correctly coded for the request for the engine control module / the Auxiliary Air Heater Control Module -J604- to switch on the Auxiliary Heater Heating Element -Z35- and for the Auxiliary Heater Control Module -J364- for the parking heater to operate as an auxiliary heater. use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

The correct request for the Climatronic Control Module -J255- control head must be installed so that the request to turn on the auxiliary heater is sent to the Data bus on the Auxiliary Air Heater Control Module -J604- for vehicles with a high voltage system (hybrid vehicles) and gasoline engines. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

The test for the activation of the Auxiliary Heater Heating Element -Z35- depends on the engine version. For a vehicle with a diesel engine, this can be found in the Guided Fault Finding for the engine installed in this vehicle. For a vehicle with a gasoline engine, this is found in the guided fault finding for the A/C system. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Currently installed Auxiliary Air Heater Control Module -J604- for vehicles with a specific gasoline engine, is not diagnostic-capable. use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

-- So that the Climatronic Control Module -J255- sends a request to turn on the auxiliary heater via the data bus to the Engine Control Module (ECM, the following requirements, for example, must be fulfilled on vehicles with a TDI engine:

Engine is running for a minimum of eight seconds and engine speed is greater than 500 RPM.
Engine temperature is less than 75 °C (167 °F).
The calculated outside air temperature is lower than 8 °C (46.4 °F).
The electrical system voltage is greater than 12.2 volts and no request that forbids the switch-on is sent by Vehicle Electrical System Control Module -J519-.
No malfunction is stored in the Climatronic Control Module -J255-.
No fault is stored in ECM and the generator load is less than 30 to 77% (depending on engine speed, only for the activation of the Auxiliary Heater Heating Element -Z35-).
On the basis of the setting and the measured temperatures, the Climatronic Control Module -J255- calculated that additional heat output is necessary to achieve the intended passenger compartment temperature.
The Climatronic Control Module -J255- calculated that more than 90% of the air is guided through the heater core of the A/C unit.
No errors are recognized by the ECM at the Auxiliary Heater Heating Element -Z35- and the Climatronic Control Module -J255- is notified via the local data bus.

Switch-Off Criteria for the Electrical Auxiliary Heater Activation

NOTE:

Activation is switched off as soon as a switch-on condition is no longer met in the Climatronic Control Module -J255- control head, or in the respective ECM or one of the switch-off criteria has been detected.

-- The Climatronic Control Module -J255- switches off the request to the switch-on for the auxiliary heater on the ECM (on the Auxiliary Air Heater Control Module -J604-).

When one of the switch-on requirements is no longer met.
The calculated outside air temperature is higher than 11 °C (51.8 °F).
The generator load is greater than 95% (only for the activation of the Auxiliary Heater Heating Element -Z35-).
The Climatronic Control Module -J255- calculated that less than 60% of air is directed through the heater core of the A/C unit (position of temperature doors).