Heater operation, function

Since the stationary heater (STH) operation depends on the circuit status, the following function requirements exist for starting the STH heater operation:

 At standstill with status "Circuit 15 OFF" and fuel tank fill level > 15 l

 At standstill with status "Circuit 15 ON", "Circuit 61 OFF" and fuel tank fill level > 15 l

At standstill with status "Circuit 15 OFF" and fuel tank fill level > 15 l

If the hot water heater booster control unit (A90) receives the switch-on signal from the heater timer (A71), the stationary heater heating mode is immediately started.

If the stationary heater heating mode is activated using the heater timer, the "VWZ_STH_MFL (pre-selection time status)" signal is sent to the hot water heater booster control unit. The hot water heater booster control unit then sends the "STHL_EIN_KOMBI (stationary heater/ventilation ON)" signal over a discrete line to the climate control control and operating unit (A81) which actuates the front blower motor (M4).

At standstill with status "Circuit 15 ON", "Circuit 61 OFF" and fuel tank fill level > 15 l

With status "Circuit 15 ON", the hot water heater booster control unit is activated. If the hot water heater booster control unit does not receive a switch-on signal, the hot water heater booster control unit switches to "sleep mode" again. Only after the hot water heater booster control unit receives the switch-on signal from the heater timer is the stationary heater heating mode immediately activated.

During the stationary heater heating mode runtime, an operating period between 10 min and 120 min or continuous operation can be selected. The STH heater operation is subdivided into the following 4 sections:

 Startup phase

 Heating mode

 Control mode

 Run-on

Startup phase

During the startup phase, the hot water heater booster control unit actuates the glow pin (A90r18) and the blower motor (A90m46) of the stationary heater combustion air blower. The climate control control and operating unit actuates the circulation pump (M51) or circulation pump (M60) with CODE HZ5 (Auxiliary water heater 10 kW with timer). The glow pin provides the preheating, the blower motor of the stationary heater combustion air blower provides the ventilation of the combustion chamber with downpipe and the circulation pump or circulation pump with CODE HZ5 (Auxiliary water heater 10 kW with timer) ensures that the coolant is circulated. After t = 5 s, actuation of the blower motor for the stationary heater combustion air blower is interrupted and the vehicle's front blower motor is actuated by the climate control control and operating unit. After t = 35 s, the blower motor for the stationary heater combustion air blower is actuated again, and after t = 42 s the metering pump (M61) is actuated by the hot water heater booster control unit. The blower motor of the STH 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 heater booster control unit recognizes correct combustion in the combustion chamber with downpipe through the flame sensor (A90b96) after t = 120 s, the stationary heater unit then switches to "heating mode". If the hot water heater booster 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, the start procedure of the stationary heater unit is repeated in the described manner. If the hot water heater booster 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 stationary heater unit fault shutoff takes place and the stationary heater unit switches to run-on.

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

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

Heating mode

During heating mode, the hot water heater booster control unit interrupts actuation of the glow pin and continuously regulates the blower motor of the stationary heater 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 or the circulation pump with CODE HZ5 (Auxiliary water heater 10 kW with timer) and the vehicle's front blower motor. The stationary heater unit is now set to power output stage "High (5 kW)". Depending on the actuation by the hot water heater booster control unit during heating mode, the heating mode is regulated to "control mode" in the power output stages "High (5 kW)" or "Low (2.4 kW)".

Control mode

During the control mode, the hot water heater booster control unit actuates the following components depending on the output stage required, "High (5 kW)" or "Low (2.4 kW)":

 Blower motor of the STH combustion air blower

 Metering pump

If the coolant temperature increases to > 85 °C although the power output stage is set to "Low (2.4 kW)", then the stationary heater unit switches to a control break. During the control pause, the actuation of the blower motor for the stationary heater combustion air blower and the metering pump is interrupted by the hot water heater booster control unit, and the stationary heater unit switches into run-on mode for t = 130 s. The circulation pump or the circulation pump with CODE HZ5 (Auxiliary water heater 10 kW with timer) 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 STH combustion air blower and the metering pump are actuated again and the stationary heater unit switches to control mode again. To this end, the hot water heater booster control unit receives the signals from the following components over a discrete line:

 Temperature sensor (A90b97)

 Temperature selection switch

If the hot water heater booster control unit recognizes a flame-out during the heating mode or the control mode through the flame sensor, then the start of the stationary heater unit is repeated in the manner described. If, after a restart, the hot water heater booster 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 stationary heater unit fault shutoff takes place and the stationary heater unit switches to the run-on mode.

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

If the hot water heater booster control unit in heating mode or control mode recognizes overheating (> 90 °C) of the stationary heater unit through the overheating sensor (A90b98), then actuation of the metering pump is interrupted, a stationary heater unit fault shutoff takes place and the stationary heater unit switches to run-on mode. After the reason for the overheating has been rectified and the stationary heater unit has cooled down (< 70 °C), the start of the heating mode can be restarted by switching the stationary heater unit on and off. During the startup phase, in heating mode and in control mode, the speed of the blower motor for the stationary heater combustion air blower is monitored by the hot water heater booster control unit. If the blower motor for the stationary heater combustion air blower does not start up or if the speed drops below 40 % of the specified speed, then after t = 60 s a stationary heater unit fault shutoff takes place and the stationary heater unit switches to the run-on mode.

Terminate STH heater operation

The stationary heater heating mode is ended after expiration of the preset operating time, after a status change from "Circuit 15 ON" to "Circuit 15 OFF" or after the switch-off signal is received by the hot water heater booster control unit from the heater timer.

After STH heater operation has ended, the stationary heater unit switches to run-on mode.

Run-on

During run-on, the hot water heater booster control unit actuates the blower motor for the stationary heater 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 or the circulation pump with CODE HZ5 (Auxiliary water heater 10 kW with timer) for t = 120 s. The blower motor of the stationary heater combustion air blower is used to cool off the stationary heater unit's combustion chamber with downpipe through the generated air suction and to discharge combustion gases. The circulation pump or the circulation pump with CODE HZ5 (Auxiliary water heater 10 kW with timer) is used to cool down the heat exchanger of the stationary heater unit using the blowby coolant. The glow pin burns itself off during this time.