Starting heater booster, function

P83.70-0413-09

1 Burner housing

2 Heat exchanger

A1 Instrument cluster

A6m2 Combustion air blower

M13 Coolant circulation pump

S4/3 Heater booster switch

Y23 Fuel metering pump

A6n1 Heater booster control module

A6r2 Glow pin

G2 Generator

Function sequence

1 The vehicle engine is started. The coolant circulation pump (M13) pumps the coolant through the heat exchanger (2). Positive voltage from the generator (G2), circuit 61 (charge indicator) is connected to the instrument cluster.

2 Heater booster switch (S4/3) in position "heater booster on", red LED in switch not burning.

3 The instrument cluster recognizes that the engine has been started and checks the temperature of the coolant and outdoor air for operation of the heater booster.

4 Coolant temperature 73 °C

Outdoor air temperature  8 °C

The instrument cluster recognizes from the temperatures of the coolant and outdoor air that operation of the heater booster is required. The instrument cluster starts up the heater booster by switching positive voltage to the heater booster control module (A6n1) across the closed switching contact of the heater booster switch (S4/3).

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5 The combustion air blower (A6m2) runs at approximately full load speed.

6 The check of the flame monitor is started for 2 s, acting as a flame monitor the glow pin (A6r2) indicates:

 "cold" = no flame present  start is continued.

 "hot" = flame present  start is interrupted due to a defect in the glow pin (malfunction switch-off).

7 The glow pin is switched on. The preglow time of approx.
40 s starts.

8 The preglow time is terminated, the combustion air blower (A6m2) is switched off for 3 s and the fuel metering pump (Y23) starts pumping fuel.

9 The combustion air blower (A6m2) starts again. The speed increases during the next 60 s to the medium speed range. The fuel metering pump (Y23) pumps at its lowest output. The fuel and the combustion air form a fuel/air mixture in the burner housing (1).

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10 After the 60 s period a stabilization period for flame formation starts for approx. 15 s. The combustion air blower runs constantly in the medium speed range during this period.

11 After completion of the stabilization time the combustion air blower and fuel metering pump increase their speed and output to nearly full load operation during the next 50 s.

12 After the increase in the combustion air and fuel supply is completed, the glow pin is switched off and a safety time for checking the flame of approx. 45 s starts:

 The glow pin assumes the function of flame monitor for checking the flame.

13 After completion of the safety time the glow pin signals:

 "hot" = sufficient flame formation  heating operation continues.

 "cold" = flame formation not present or insufficient  the fuel metering pump (Y23) is switched off and the start-up procedure repeated once.

13 After combustion has stabilized the combustion air blower and fuel metering pump operate at maximum speed and output. The heat is transferred in the heat exchanger (2) and the coolant temperature increases.