Heater operation, function

Function requirements, general

 "Circuit 61 ON" through circuit D+ relay (K26)

As soon as the hot water auxiliary heater control unit (E90) receives the switch-on signal from the air conditioning, heater booster, residual heat rotary switch in the climate control and operating unit (A81) with CODE HH9 (Regulated air conditioning (Tempmatic)) or from the heater booster rotary switch in the climate control control and operating unit, except CODE HH9 (Regulated air conditioning (Tempmatic)), the heater booster (HB) heating mode is immediately started. Activation of the heating mode on the heater booster heater unit is indicated by the LED next to the symbol lighting up.

 The air conditioning, heater booster, residual heat rotary switch in the climate control control and operating unit with CODE HH9 (Regulated air conditioning (Tempmatic)) or the heater booster rotary switch in the climate control control and operating unit, except CODE HH9 (Regulated air conditioning (Tempmatic)) has a "memory function" (automatic triggering of heating mode in heater booster heater unit). The "memory function" remains active until it is deactivated again by operating the air conditioning, heater booster, residual heat rotary switch in the climate control control and operating unit with CODE HH9 (Regulated air conditioning (Tempmatic)) or the heater booster rotary switch in the climate control control and operating unit, except CODE HH9 (Regulated air conditioning (Tempmatic)).

The runtime of the heater booster heater unit heating mode is unlimited until the status changes to "Circuit 61 OFF". The heating mode of the heater booster heater unit is divided up into the 4 following sections:

 Startup phase

 Heating mode

 Control mode

 Run-on

Startup phase

During the startup phase, the hot water auxiliary heater control unit actuates the glow pin (E90r18) and the blower motor (E90m46) for the heater booster combustion air blower. The circulation pump (M51) is actuated by the climate control control and operating unit when the heating mode is started.

The glow pin provides the preheating, the blower motor for the heater booster combustion air blower provides the ventilation of the combustion chamber with downpipe and the circulation pump circulates the coolant. After t = 5 s, actuation of the blower motor of the heater booster combustion air blower is interrupted. After t = 35 s, the blower motor for the heater booster combustion air blower is actuated again and after t = 42 s the metering pump (M61) is actuated by the hot water auxiliary heater control unit. The blower motor of the heater booster combustion air blower is responsible for the supply of combustion air and the metering pump ensures the supply of fuel. The supplied combustion air and the supplied fuel form an ignitable mixture, which is ignited at the glow pin. If the hot water auxiliary heater control unit recognizes correct combustion in the combustion chamber with downpipe through the flame sensor (E90b96) after t = 120 s, the heater booster heater unit then switches to the heating mode.

If the hot water auxiliary heater control unit does not detect correct combustion in the combustion chamber with downpipe via the flame sensor after fuel has been supplied for t = 90 s, the start procedure of the heater booster heater unit is repeated in the described manner. If the hot water auxiliary heater control unit does not detect correct combustion in the combustion chamber with downpipe through the flame sensor after fuel has been supplied for another t = 90 s, a heater booster heater unit fault shutoff takes place and the heater booster heater unit switches to run-on.

 After an impermissible number of heater booster heater unit fault shutoffs, the hot water auxiliary heater control unit is locked.

 If the glow pin is defective or the electrical line of the metering pump is interrupted, the heater unit heater booster will not start.

Heating mode

During heater operation, the hot water auxiliary heater control unit interrupts actuation of the glow pin and continuously regulates the blower motor for the heater booster combustion air blower and the metering pump to a higher output. The ignitable mixture will now automatically ignite at the hot walls of the combustor with downpipe. The climate control control and operating unit continues to actuate the circulation pump. The heater unit heater booster is now set to power output stage "High (5 kW)". During heater operation, depending on the actuation by the warm water auxiliary heating control unit, heater operation is regulated to "Control mode" in the power output stages "High (5 kW)" or "Low (2.4 kW)".

Control mode

During control mode, the warm water auxiliary heating control unit actuates, depending on the required power output stage "High (5 kW)" or "Low (2.4 kW)", the following components:

 Blower motor of heater booster combustion air blower

 Metering pump

The control mode is dependent on the temperature value, which is set using the temperature selector switch integrated into the climate control control and operating unit. The switch-on requirement for the heater unit heater booster is a coolant temperature of < 75 °C. At a coolant temperature of > 80 °C, the setting of the heater booster heater unit is reduced to power output stage "Low (2.4 kW)".

If the coolant temperature increases to > 85 °C although the power output stage is set to "Low (2.4 kW)", the heater unit heater booster switches to a control break. During the control pause, the actuation of the blower motor for the heater booster combustion air blower and the metering pump is interrupted by the hot water auxiliary heater control unit, and the heater booster heater unit switches into run-on mode for t = 130 s. The circulation pump continues to be actuated by the climate control control and operating unit. If the coolant temperature drops to < 75 °C, the blower motor of the heater booster combustion air blower and the metering pump are actuated again and the heater unit heater booster switches to control mode again. To this end, the hot water auxiliary heater control unit receives the messages from the following component over a discrete line:

 Temperature sensor (E90b97)

If the hot water auxiliary heater control unit recognizes a flame-out during the heating mode or the control mode through the flame sensor, then the start of the heater booster heater unit is repeated in the manner described. If, after a restart, the hot water auxiliary heater control unit does not detect correct combustion in the combustion chamber with downpipe through the flame sensor after fuel has been supplied for t = 90 s, or if the flame goes out after t = 15 min after the heater has been operated again, a heater booster heater unit fault shutoff takes place and the heater booster heater unit switches to the run-on mode.

 This heater booster heater unit fault shutoff can be canceled a maximum of 2 times by switching the heater booster heater unit on and off.

If the hot water auxiliary heater control unit recognizes overheating of the heater booster heater unit (> 90 °C) through the overheating sensor (E90b98) in heating mode or in control mode, actuation of the metering pump is interrupted. There is a fault shutoff of the heater booster heater unit and the heater booster heater unit switches to run-on mode. After the reason for the overheating has been rectified and the heater booster heater unit has cooled down (< 70 °C), the heating mode can be restarted by switching the heater booster heater unit on and off. During the startup phase, in heating mode and in control mode, the speed of the blower motor for the heater booster combustion air blower is monitored by the hot water auxiliary heating control unit.

If the blower motor for the heater booster combustion air blower fails to start or if the speed drops to less than 40 % of the specified speed, after t = 60 s a heater booster heater unit fault shutoff takes place and the heater booster heater unit switches to run-on.

End heater booster heater unit heating mode

The heating mode of the heater booster heater unit is ended after a status change from "Circuit 61 ON" to "Circuit 61 OFF" or by turning the air conditioning, heater booster, residual heat rotary switch in the climate control control and operating unit with CODE HH9 (Regulated air conditioning (Tempmatic)) or the heater booster rotary switch in the climate control control and operating unit, except CODE HH9 (Regulated air conditioning (Tempmatic)) to another position.

 The air conditioning, heater booster, residual heat rotary switch in the climate control control and operating unit with CODE HH9 (Regulated air conditioning (Tempmatic)) or the heater booster rotary switch in the climate control control and operating unit, except CODE HH9 (Regulated air conditioning (Tempmatic)) has a "memory function" (automatic triggering of heating mode in heater booster heater unit). The "memory function" remains active until it is deactivated again by operating the air conditioning, heater booster, residual heat rotary switch in the climate control control and operating unit with CODE HH9 (Regulated air conditioning (Tempmatic)) or the heater booster rotary switch in the climate control control and operating unit, except CODE HH9 (Regulated air conditioning (Tempmatic)).

The circulation pump is used to cool down the heat exchanger of the heater booster heater unit using the blowby coolant. The glow pin burns itself off during this time. After heater operation has ended, the heater unit heater booster switches to power-down mode.

Run-on

During run-on, the hot water auxiliary heater control unit actuates the blower motor for the heater booster combustion air blower for t = 120 s and the glow pin for t = 20 s. The climate control control and operating unit actuates the circulation pump for t = 120 s. The blower motor for the heater booster combustion air blower is used to cool down the combustion chamber with downpipe for the heater booster heater unit by the generated air suction and to discharge combustion gases.