"Heater operation", function

P83.70-3349-09

1 Data bus (CAN-C)

2 Burner housing

3 Heat transfer unit

4 Coolant pump, mechanical

A6m2 Combustion air blower

A6n1 Heater booster control module

S25/18 Air temperature switch
(up to 31.05.00)

Y23 Heater booster fuel metering pump

A Control as of 01.06.00

B Control up to 31.05.00

B14 Ambient temperature indicator temperature sensor

G2 Generator

N10/6 Left front SAM control module

N10/7 Right front SAM control module

S4/3 Heater booster switch

Operating procedure

1 The start of the heater booster operation is completed:

 The vehicle engine's mechanical coolant pump (4) delivers the coolant by way of the heat transfer unit (3) and the heating and cooling circuits.

 Combustion is steady, the coolant is heated up.

2 Coolant temperature < 72 °C

 The heat requirement is high:
 The heater is operating at full load, the combustion air blower (A6m2) and fuel metering pump (Y23) deliver at their maximum speeds or outputs.

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3 The coolant temperature in full-load operation reaches 72 °C

Heat requirements < than the momentary available heating output:

 The heating output can be reduced.

 The heater booster control module (A6n1) initiates a load change from full load to part-load operation:

 The HB fuel metering pump and the combustion air blower are switched within 50 s in continuously variable steps to part-load operation and from then on deliver again at their lowest outputs and speeds.

 The coolant temperature remains constant or drops depending upon the heat requirements.

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4 The coolant temperature drops to below 65 °C in part-load operation

Heat requirements > than the momentary available heating output:

 The heating output is too low and has to be increased again.

 The Heater booster control module initiates a load change from part-load to full-load operation :

 The ZUH fuel metering pump and the combustion air blower are switched within 50 s in continuously variable steps to full-load operation and from then on deliver at their highest outputs and speeds.

 The coolant temperature increases again.

 The change between full-load and part-load operation continues for the entire duration of the heater operation or until the heat requirements change.