HEATING AND VENTILATION (Description): DESCRIPTION AND OPERATION (page 10 of 10)

HEATING AND VENTILATION

80-12

DESCRIPTION AND OPERATION

Burner housing. The burner housing contains the burner insert and also incorporates connections for the exhaust 
pipe, the coolant inlet from the circulation pump and the coolant outlet to the heater assembly. The exhaust pipe 
directs exhaust combustion gases to atmosphere at the bottom of the engine compartment.

The burner insert incorporates the fuel combustion chamber, an evaporator and a glow plug/flame sensor. Fuel from 
the FBH fuel pump is supplied to the evaporator, where it evaporates and enters the combustion chamber to mix with 
air from the combustion air fan. The glow plug/flame sensor provides the ignition source of the fuel:air mixture and, 
once combustion is established, monitors the flame.

ECU/heat exchanger.  The ECU controls and monitors operation of the FBH system. Ventilation of the ECU is 
provided by an internal flow of air from the combustion air fan. The heat exchanger transfers heat generated by 
combustion to the coolant. A sensor in the heat exchanger provides the ECU with an input of heat exchanger casing 
temperature, which the ECU relates to coolant temperature and uses to control system operation. The temperature 
settings in the ECU are calibrated to compensate for the difference between coolant temperature and the heat 
exchanger casing temperature detected by the sensor. Typically: as the coolant temperature increases, the coolant 
will be approximately 7 

°

C (12.6 

°

F) hotter than the temperature detected by the sensor; as the coolant temperature 

decreases, the coolant will be approximately 2 

°

C (3.6 

°

F) cooler than the temperature detected by the sensor.