Starting up heater operation at coolant temperature between 77 – 83 °C, function

P83.70-0390-09

1 Burner housing

2 Heat exchanger

3 Heater circuit thermostat

A6m1 Circulation pump

A6m2 Combustion air blower

Y23 Stationary heater fuel metering pump

B Thermostat position with auxiliary circuit open

A6n1 Stationary heater/heater booster control module

A6r2 Glow pin

N22 Pushbutton control module (automatic/A/C)

N34 Stationary heater timer

Operation

1 Coolant temperature > 59 °C :
The thermostat (3) is switched to heater operation, the auxiliary circuit for the stationary heater is connected to the vehicle cooling and heating circuit.

2 The green indicator lamp in the stationary heater timer (N34) comes on. The stationary heater is started up.

3 The combustion air blower (A6m2) and circulation pump (A6m1) start running. The combustion air blower operates at nearly full load speed.The coolant flows through the vehicle cooling and heating circuit.

4 Coolant temperature > 30 °C :
The A/C pushbutton control module (N22) switches on the vehicle heater blower.

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5 The flame monitor is checked for 1 s, the glow pin (A6r2) functions as a flame monitor and indicates:

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

 "hot" = flame present  start-up is terminated due to defective glow pin (malfunction shut-off).

6 The glow pin (A6r2) is switched on. The preglow time of approx. 30 s starts.

7 After completion of the preglow time the combustion air blower (A6m2) stops running for 3 s and the fuel metering pump (Y23) starts pumping fuel.

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8 The combustion air blower (A6m2) starts running again. The combustion air blower and fuel metering pump increase their output to full load within the next 60 s. The fuel and combustion air form the fuel/air mixture in the burner housing (1).

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

 The glow pin acts as a flame monitor to check the flame.

10 The safety time is completed and the glow pin reports:

 "hot" = sufficient flame formation  heating operation is continued.

 "cold" = no flame present or flame formation insufficient  the fuel metering pump (Y23) is switched off and the start-up operation is repeated once.

11 Combustion has stabilized. Heat is exchanged in the heat exchanger (2).

12 Heat requirement < heater output present momentarily

Coolant temperature > 77 °C

13 The stationary heater control module (A6n1) recognizes from the coolant temperature that the heater output momentarily present is not required and switches over from full load to partial load.

14 The fuel metering pump (Y23) and the combustion air blower (A6m2) are switched over to partial load within 50 s and then operate at their lowest output and speed. The heater output is reduced, the coolant temperature remains constant or decreases if the heat requirement then increases.