"Heater operation", function

P83.70-2221-09

1 Burner housing

2 Heat transfer unit

3 CAN bus

A6/1 STH radio remote control receiver

N22 AAC pushbutton control module

S46 Emergency STH control switch

Y23 STH fuel metering pump

A6m1 Circulation pump

A6m2 Combustion air blower

A6n1 STH control module

Operating procedure

1 The start of the heater operation is completed:

 The green indicator light in the emergency c control switch (S46) illuminates.

 Coolant temperature > 30 °C :
The vehicle blower is switched on, controlled by the AAC pushbutton control module (N22).

 The circulation pump (A6m1) delivers the coolant via the heat transfer unit (2) and the heating and cooling circuits. Combustion is steady, the coolant is heated up and dissipates the heat by way of the vehicle heating into the cold passenger compartment.

2 Coolant temperature < 70 °C

The heat requirement is high:

The heater is operating at full load, the combustion air blower (A6m2) and STH fuel metering pump (Y23) deliver at their maximum speed or output.

-----------------------------------------------------------------------------------------

3 Coolant temperature  77 °C

Heat requirements < than the momentary available heating output:

 The heating output is too high and must be reduced in order to prevent it from overheating.

 The STH control module (A6n1) recognizes this on account of the coolant temperature value and initiates a load change from full load to part-load operation.

 The STH fuel metering pump (Y23) and the combustion air blower (A6m2) are switched within 50 s in continuously variable steps to part-load operation and from then on deliver at their lowest outputs and speeds. The coolant temperature remains constant or drops depending upon the heat requirements.

-----------------------------------------------------------------------------------------

4 Coolant temperature  68 °C

Heat requirements > than the momentary available heating output:

 The heating output is too low and has to be increased again.

 The STH control module (A6n1) recognizes that the heating output is too low on account of the coolant temperature value and initiates a load change from part-load to full-load operation.

 The STH fuel metering pump (Y23) and the combustion air blower (A6m2) are switched within 50 s in continuously variable steps to full-load operation and from then on deliver at their highest outputs and speeds. The coolant temperature increases again.

 The change between part-load and full-load operation continues for the entire duration of the heater operation until the heat requirements change.

5 Coolant temperature  83 °C

Heat requirements < than the momentary available heating output:

 Heating output is not required. The heater is already operating in part-load mode, however the coolant temperature continues to rise and the heater threatens to overheat.

 The STH control module (A6n1) recognizes that there is a danger of overheating on account of the coolant temperature value and immediately switches the STH fuel metering pump off (Y23). Combustion is interrupted.

 The heater afterrun which serves to cool the heater and purge the combustion chamber runs for approx. 160 s. At the end of the afterrun period the combustion air blower (A6m2) is switched off. The heater now enters a so-called combustion interval. The circulation pump (A6m1) and the vehicle blower continue to run and coolant temperature drops. As soon as the coolant temperature reaches 75 °C and the heating period is not yet completed, a restart with flame monitor query, glow time and safety time is automatically initiated.