Starting up heater operation at coolant temperature of > 83 °C, function

P83.70-0390-09

1 Burner housing

2 Heat exchanger

3 Heizkreis-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).

No heat requirement or heat requirement low

12 The heater output is too high, the coolant temperature increases to above 83 °C. It is necessary to reduce the heater output to protect against overheating.

13 The stationary heater control module (A6n1) recognizes from the coolant temperature that the heater output is too high and switches the fuel metering pump off immediately. The combustion is interrupted due to the absence of fuel.

14 The stationary heater shut-off delay of approx. 170 s is started to cool down the heater and purge the combustion chamber. The combustion air blower reduces its speed during the first 40 s of the shut-off delay period to partial load and then increases it again to virtually full load speed.

15 After completion of the heater shut-off delay the combustion air blower is switched off, the circulation pump (A6m1) and the vehicle blower continue to run. The heater is in the stand-by mode and the coolant temperature decreases.

16 Coolant temperature decreases to below 75 °C.
The heat requirement increases and the stationary heater control module (A6n1) automatically restarts the heater with flame monitor check, preglow time and safety time.