Auxiliary heater

Auxiliary heater

1.	Blower fan

2.	Blower fan, engine

3.	Heat exchanger

4.	Combustion chamber

5.	Glow plugs

6.	Flame detector

7.	Coolant temperature sensor 1

8.	Coolant temperature sensor 2

9.	Control module

10.	Air intake

11.	Exhaust pipe

12.

Fuel pump

13.	Fuel filter

14.

Fuse

15.	8-pin connector

16.	Coolant outlet

17.	Coolant inlet

Operating functions

The heater combustion chamber is positioned so that it is completely surrounded by the heat exchanger, which means that the heat energy is utilised very efficiently.

The diesel heater has a fan that controls the induction of air into the combustion chamber and that, together with the fuel pump, controls the heater output.

When the heater starts, the fan operates at max. output and cold blows the combustion chamber, then the glow plug is activated. Approximately 40 seconds after glow plug activation, the fuel pump starts at half speed and then the fan starts and gradually increases in speed to half speed.

When the flame temperature sensor signals that combustion has started (temperature in combustion chamber exceeds 80°C (176°F)) the fan and pump run at full speed and the heater operates at full power, i.e. 3000 W.

When the control module receives a signal from coolant temperature sensor 1 that the coolant has reached 80°C (176°F), the pump and fan decrease to half speed and heater output is lowered to 1500 W. If the coolant temperature drops below 75°C (167°F), the heater returns to full power. If the coolant temperature exceeds 85°C (180°F), the heater will shut off. If the temperature subsequently drops below 75°C (167°F), the heater will start again.

Safety functions

Before start, the blower fan will cold blow the combustion chamber. If the temperature of the combustion chamber should not drop below 70°C (158°F) within 240 seconds, the heater will shut off.

If the control module does not receive a signal from the flame temperature sensor that the flame has been ignited (temperature in combustion chamber exceeds approximately 80°C (176°F) for 120 seconds) the start attempt is interrupted. A new attempt is permitted but if this fails as well, no further attempts are made during that driving cycle. If 10 start attempts have failed, the heater is blocked and no start attempts are permitted before the diagnostic trouble codes have been deleted.

Should the temperature difference between the coolant temperature sensors exceed 25°C (77°F) , due to insufficient flow through the heater, for example, the control module reacts and interrupts operation before critical temperature levels are reached.

If any of the sensors detects a temperature exceeding 125°C (257°F) , the control module shuts down the fuel pump. If the temperature should continue to increase to 130°C (266°F), the control module cuts off the power to the fuel pump drive, if this has not previously been done by the control module microprocessor.

If 10 overheatings have been registered, the heater is blocked and no further start attempts are permitted before the diagnostic trouble codes are removed.