Increase in outdoor air temperature during partial load or full load operation, function

P83.70-0422-09

1 Burner housing

2 Heat exchanger

A1 Instrument cluster

M13 Coolant circulation pump

S4/3 Heater booster switch

Y23 Fuel metering pump

A6m2 Combustion air blower

A6n1 Heater booster control module

G2 Generator

Function sequence

1 Coolant temperature < 82 °C

Outdoor air temperature  8 °C

The vehicle engine runs and the instrument cluster (A1) is actuated by the generator (G2) via circuit 61 (charge indicator).

2 Heater booster switch (S4/3) in position "heater booster on", red LED in switch not burning. Positive potential is present on the heater booster control module (A6n1) from the instrument cluster via the closed switching contact of the switch.

3 The heater operates at partial load or full load depending on the coolant temperature, the coolant circulation pump (M13) pumps coolant through the heat exchanger (2). The fuel metering pump (Y23) and combustion air blower (A6m2) operate at partial or full load output and speed.

4 The outdoor air temperature increases to above 8 °C. The instrument cluster interrupts the positive signal to the control module (A6n1) shutting off the heater booster.

5 The fuel metering pump is switched off and the combustion in the burner housing (1) interrupted due to lack of fuel.

6 The heater shut-off delay starts for cooling down the heater and purging the combustion chamber. The duration of the shut-off delay depends on the heater mode present when the engine was shut off:

 Partial load = shut-off delay approx. 110 s

 Full load = shut-off delay approx. 175 s

7 After completion of the heater shut-off delay the combustion air blower is switched off.

8 Operation of the heater booster is terminated. The coolant circulation pump (M13) continues to pump coolant through the heat exchanger (2) although the heater is switched off.