Heater mode, function

S83.70-2525-06

Heater booster

1 Jacket

2 Coolant inlet

3 Coolant outlet

4 Heater core

5 Burner housing

A90 Heater booster

A90.1 Main wiring harness connector to heater booster

A75 Heater booster control module

A75.3 Heater booster connector in electric compartment

B94 Coolant temperature switch

B95 Overheating fuse

B96 Flame monitor

M44 Combustion air blower

M54 Heater booster fuel metering pump

R18 Glow plug

S83.70-2521-06

Heater booster

1 Jacket

2 Coolant inlet

3 Coolant outlet

4 Heater core

5 Burner housing

A34 Hot water auxiliary heater

A34.1 Main wiring harness connector to auxiliary heater

A34.2 Water pump auxiliary heater connector

A87 Hot water auxiliary heater with heater booster function

A87.1 Main wiring harness connector to auxiliary heater with heater booster function

A87.2 Water pump connector auxiliary heater

A72 Auxiliary heater control module

A72.3 Auxiliary heater connector in electric compartment

A74 Auxiliary heater control module with heater booster function

A74.3 Auxiliary heater connector with heater booster function in electric compartment

B94 Coolant temperature switch

B95 Overheating fuse

B96 Flame monitor

M19 Auxiliary heater fuel metering pump

M44 Combustion air blower

R18 Glow plug

A) Heat requirement < 50 % of heating capacity

Function sequence

1 The start of the heating mode is completed. The combustion air blower (M44) and the fuel metering pump (M19/M54) operate at partial load at their lowest output.

2 The coolant temperature increases to above 86 °C.

Heat requirement < momentary heater output

3 The coolant temperature continues to increase. The hot water auxiliary heater (A34/A87) or the heater booster (A90) can overheat. It is necessary to reduce the heater output.

4 The fuel metering pump (M19/M54) is switched off interrupting the combustion.

5 The shut-off delay for cooling the heater and purging the combustion chamber starts for approx. 120 s. The combustion air blower (M44) runs for approx. 25 s at partial load and for approx. 95 s at full load.

6 The shut-off delay is completed. The combustion air blower (M44) is switched off, the circulation pump and the blower in the vehicle heater continue to run. The heater is now in the combustion pause, the coolant temperature drops.

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7 The coolant temperature drops to below 77 °C.

Heat requirement > momentary heater output

8 The heater is started automatically with preglowing time of approx. 32 s, safety time of approx. 85 s and stabilization time of approx. 20 s.

9 After the stabilization time the fuel metering pump (M19/M54) and the combustion air blower (M44) are switched to full load. The coolant temperature increases.

10 The coolant temperature increases to above 79 oC.

Heat requirement < momentary heater output

11 The fuel metering pump (M19/M54) and the combustion air blower (M44) are switched to partial load and operate at their lowest output.

12 The coolant temperature continues to increase to above
86 °C. The heater can overheat. It is necessary to reduce the heater output.

13 The fuel metering pump (M19/M54) is switched off interrupting the combustion.

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B) Heat requirement between 50 and 100 % of heating capacity

Function sequence

1 The start of the heating mode is completed. The combustion air blower (M44) and the fuel metering pump (M19/M54) operate at partial load at their lowest output.

Heat requirement > momentary heater output

2 The coolant temperature drops. It is necessary to increase the heater output.

3 The fuel metering pump (M19/M54) and the combustion air blower (M44) are switched to full load and operate at their maximum capacity. The combustion air blower (M44) increases its speed infinitely within approx. 60 s.

4 The heater operates at full load, the coolant temperature increases.

5 The coolant temperature increases to above 79 °C.

Heat requirement < momentary heater output

6 The coolant temperature increases. It is necessary to reduce the heater output.

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7 The fuel metering pump (M19/M54) and the combustion air blower (M44) switch to partial load operation. The combustion air blower (M44) reduces its speed infinitely within approx. 60 s

8 The heater operates at partial load operation, the coolant temperature drops.

9 The coolant temperature drops to below 72 °C.

Heat requirement > momentary heater output

10 The coolant temperature continues to decrease. It is necessary to increase the heater output again.

11 The fuel metering pump (M19/M54) and the combustion air blower (M44) are switched back to full load.

12 The heater operates at full load, the coolant temperature increases.

 The system alternates continuously between partial load and full load for the entire heating period as long as the heat requirement remains unchanged.

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B) (Continuation)

14 The shut-off delay for cooling the heater and purging the combustion chamber starts for approx. 120 s. The combustion air blower (M44) runs for approx. 25 s at partial load and for approx. 95 s at full load.

15 The shut-off delay is completed. The combustion air blower (M44) switches off, the circulation pump and the blower for the vehicle heater continue to run. The heater is again in the combustion pause, the coolant temperature drops.

 As soon as the coolant temperature drops to below 77 °C the heater starts up automatically. Then it switches to full load and, if the heat requirement remains constant, to partial load followed by a combustion pause to protect against overheating.

The system alternates continuously between heating mode and combustion pause until the end of the heating period as long as the heat requirement does not change.

C) Heat requirement between 50 and 100 % of heating capacity

Function sequence

1 Heater start-up is completed. The combustion air blower (M44) and fuel metering pump (M19/M45) operate at full load at their maximum output.

Heat requirement > momentary heater output

2 The coolant temperature remains permanently below 79 °C due to the high heat requirement. The heat requirement requires uninterrupted maximum heater output.

As long as the heat requirement does not change the heater operates permanently at full load.