| Functional description of auxiliary heater |
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| The auxiliary heater is activated and deactivated by the control unit in dash panel insert -J285- by way of the “Immediate on” function and at a pre-set time (“Timer” function). |
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| If, on vehicles with air conditioner, the “auxiliary heating/auxiliary ventilation” function is activated by way of the “Timer” function by the control unit in dash panel insert -J285- or via remote control, the operating and display unit, Climatronic control unit -J255- of the air conditioner determines on the basis of the set “specified temperatures” and the measured “actual temperature” whether auxiliary heating is switched on or just the “auxiliary ventilation” function is activated. |
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| If, on vehicles with no air conditioner (heater only), auxiliary heating/auxiliary ventilation is activated by way of the “Timer” function by the control unit in dash panel insert -J285- or via remote control, it depends on the version of the control unit in dash panel insert -J285- whether the last mode selected by way of the “Immediate on” function is actuated or “Auxiliary heating” mode is always activated (not determined by operating and display unit, Climatronic control unit -J255- in this case). |
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| On vehicles on which the auxiliary heater is actuated as supplementary heater (only applies at present to vehicles with diesel engine), the operating and display unit, Climatronic control unit -J255- of the air conditioner/heater effects actuation (by way of the convenience data bus system) if additional heat output is required to obtain the temperature set in the passenger compartment. On vehicles with air conditioner, this function can be deactivated at any time by pressing the “Econ” button on the operating and display unit, Climatronic control unit -J255- of the air conditioner if additional heat output is not required (not possible at present for vehicles with heater). |
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| Depending on the amount of heat generated by the auxiliary heater (and engine) and emitted by the heat exchangers of the air conditioner unit/heater, the heater may remain for a lengthy period in full load, part load (control mode) or control interval status → Chapter and → Chapter. |
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| To assist the engine coolant pump, the circulation pump -V55- can also be activated with the auxiliary heater switched off → Chapter. |
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| The following applies to vehicles on which the auxiliary heater is actuated as supplementary heater: As the auxiliary heater is operated with the engine running, it is hardly noticeable during heating operation. If the engine is switched off, heater run-on is audible if it was in operation when the engine was switched off. |
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| The temperature sensor -G18- (for detecting the temperature of the coolant in the auxiliary heater) is installed in the auxiliary heater housing. |
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| To guard against overheating, the glow plug for heater -Q9- is actuated with a regulated voltage. |
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| To ensure best possible combustion in the heater, the metering pump -V54- (clock frequency) and combustion air blower -V6- (voltage) are regulated over the entire sequence. |
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| In auxiliary heating mode, the metering pump -V54- is actuated with full voltage by the auxiliary heater control unit -J364- up to control unit part number index “B”. For control units as of part number index “C” (gradual introduction as of Model Year 2005), the voltage for the actuation signal of the metering pump -V54- will be limited in auxiliary heating mode to 9.2 V with the petrol version and 9.8 V with the diesel version, thus reducing the operating noise of the metering pump -V54-. |
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| The temperatures given in the functional description and diagram are approximate. |
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| If the heater has been interlocked (fully deactivated) on account of a fault (e.g. “Flame interruption” or “Overheating”), it cannot be activated again until the fault memory has been read out and its content erased. |
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| If the first attempted start does not produce a flame, the auxiliary heater control unit -J364- terminates the sequence and attempts another start after any combustion residue has been blown out with the combustion air blower -V6-. The auxiliary heater control unit -J364- is deactivated if repeated starting also fails to produce a flame. |
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| If the heater is switched off during starting, the instantaneous position in the starting sequence determines whether the heater is deactivated immediately or whether run-on (burn-off, cooling) is necessary. |
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| If the coolant temperature exceeds 84 °C prior to attaining full load mode (e.g. with a hot engine), the heater switches to the control interval. |
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| Various auxiliary heater functions are constantly monitored during operation (the auxiliary heater is switched off as soon as a fault occurs). |
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| Undervoltage shutoff if the supply voltage drops below the specified shutoff voltage (e.g. on account of contact resistance in power supply) |
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| Overvoltage shutoff if the supply voltage is greater than 15.5 V for more than 6 seconds |
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| Flame interruption shutoff if the voltage at the flame monitor -G64- exceeds the specified value (e.g. flame interruption on account of a problem with the fuel supply) |
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| Overheating shutoff if the temperature of the coolant in the heater exceeds 120 °C (e.g. on account of a lack of coolant or a fault in the coolant circuit) |
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