Owing to the high efficiency of the 1.9L diesel engine, at low temperatures, there is insufficient waste heat available for the heater.
For this reason a booster heater is installed to increase the coolant temperature so that the air in the heater is heated up sufficiently.
The highest output of the booster heater is 5 kW and the lowest 2.4 kW.
A fuel pump attached to the fuel tank absorbs diesel from a separate fuel line and pumps it into the evaporator section of the combustion chamber.
The exhaust gases are discharged into the outside air by means of a separate exhaust system.
An amount of smoke during the start of the fuel fired heater is typical and a part of the normal combustion process.
The system is automatically activated when the engine is running (signal D+ from the generator is active) and when the ambient temperature is lower than 10°C and the coolant temperature falls below 75°C. The system is controlling the coolant temperature during the complete drive.
The system is not activated (or deactivated) automatically if the coolant temperature reaches 85°C and in the event of a malfunction.
A programmable control unit for the booster heater is optional, which is located in the overhead console.
Depending on the wiring the fuel fired booster heater operates as a programmable fuel fired booster heater or as a booster heater, the latter serving to compensate for a lack of heat dissipation from the vehicle engine. The programmable fuel fired booster will only function if the engine coolant temperature is below 75°C.
The switch-on time of the programmable fuel fired booster heater can be preset with the control unit for standing operation and will only run for a maximum of 30 minutes to protect the additional battery, which provides the power supply.
An additional water pump is installed between the front heater core and the engine.
Switching on
After switching on, the operation indicator in the programmable control unit illuminates. The auxiliary coolant flow pump starts up and voltage (8 V) is supplied to the glow plug. The combustion air blower is triggering for 5 seconds to check the function.
Vehicles with petrol engine:
After function check, the combustion air blower is triggered at a low rotational speed to rinse the burner with fresh air. 45 seconds after the heater is switched on, the metering pump is triggered and the combustion process begins. The combustion process continues and after 85 seconds from heater switch on (which allows the combustion process to stabilize), the glow plug is switched off.
Vehicles with diesel engine:
After function check, the combustion air blower is triggered at a low rotational speed 35 seconds after the heater is switched on to rinse the burner with fresh air. 42 seconds after the heater is switched on, the metering pump is triggered and the combustion process begins. The combustion process continues and after 120 seconds from heater switch on (which allows the combustion process to stabilize), the glow plug is switched off
If the coolant temperature rises above 30°C, the vehicle’s heater blower is switched on.
Heating mode
Depending on heat demand, the independent heating alternates between “HIGH” and “LOW” settings. The temperature thresholds are permanently programmed in the electronic control unit. If the heat demand in the “LOW” setting is so low that the engine coolant reaches a temperature of 85°C, the heater switches to the “OFF” setting, then continues to run for about 130 seconds. The control lamp is also illuminated while the heater is in the “OFF” setting, and the auxiliary coolant pump continues to run until the heater is restarted.
Switching off
When the heater is switched off, the control lamp extinguishes and fuel feed is shut off.
Vehicles with petrol engine:
The combustion air blower and the auxiliary coolant flow pump will continue to function for 50 seconds after the heater is switched off and are then switched off automatically.
Vehicles with diesel engine:
The glow plug is switched on for 20 seconds and combustion air blower and the auxiliary coolant flow pump will continue to function for 120 seconds after the heater is switched off and are then switched off automatically.
Safety devices
- • If the heater does not ignite within 90 seconds after the start of fuel feed, the start-up cycle is repeated. If the heater still does not ignite within 90 seconds after the start of fuel feed, a fault shutdown is activated.
- • If the flame extinguishes by itself while the heater is in operation, a restart is initially carried out. If the heater does not ignite within 90 seconds after the start of fuel feed, or if it ignites but extinguishes again, a fault shutdown is activated.
- • In the event of overheating, the overheat sensor is tripped and the fuel feed is shut off, then a fault shutdown is activated.
- • If the voltage drops below approximately 10 volts or rises above 16 volts, a fault shutdown is activated.
- • If the glow plug is defective or an open circuit is detected in the metering unit wiring harness, the heater does not start.
- • The blower motor speed is monitored continuously. If the blower motor does not start or becomes blocked, a fault shutdown is activated.
