C 320 Wagon (203.264) V6-3.2L (112.946) (2004)
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Component Identification
Function sequence
1. The activated heating mode is indicated by the indicator lamp in the STH switch (N72s12 or S46). The circulation pump (A6m1) delivers the
coolant via the heat exchanger (2) and the heating and cooling circuits. Combustion is steady, the coolant is heated up. The blower motor delivers,
actuated by the control and operating unit (N18, N22 or N22/7), preheated air into the interior (coolant temperature > 30 °C).
2. At coolant temperatures below 72 °C there is a high heat requirement. The STH heater unit (except model 220) or the STH or HB [ZUH] heater
unit (model 220) operates in full load mode, the combustion air blower (A6m2) and the STH fuel metering pump or the STH or HB [ZUH] fuel
metering pump (Y23) operate at their maximum rotational speed and output.
3. If in full load mode the coolant temperature reaches 72 °C, the heat requirement is less than the currently available heat output. The STH control
unit or the STH or HB [ZUH] control unit (A6n1) initiate a load change from full load to partial load mode. The STH fuel metering pump or the
STH or HB [ZUH] fuel metering pump (Y23) and the combustion air blower (A6m2) are switched continuously variably to partial load mode
within approx. 50 s and then operate at low output and rotational speed again. The coolant temperature remains constant or sinks, depending on
the heat requirement.
4. If in partial load mode the coolant temperature drops below 65 °C, the heat requirement is greater than the currently available heat output. The
heat output must be increased again. The STH control unit or the STH or HB [ZUH] control unit (A6n1) initiates a load change from partial load
to full load mode.
The STH fuel metering pump or the STH or HB [ZUH] fuel metering pump (Y23) and the combustion air blower (A6m2) are switched
continuously variably to full load mode within approx. 50 s and then operate at their maximum output and rotational speed again. The coolant
temperature increases again.
