Discovery 2. Manual — part 284

HEATING AND VENTILATION

DESCRIPTION AND OPERATION

80-7

Distribution ducts

Separate distribution ducts are installed for the front and rear footwell outlets. Distribution ducts for the face level,
windscreen and side windows outlets are integrated into the fascia. The front footwell ducts are attached to ports at
the sides of the heater assembly. The rear footwell ducts locate in ports at the rear of the heater assembly and extend
along each side of the centre console to vent into the rear footwells from below the cubby box.

Vent assemblies in the fascia allow occupants to control the flow and direction of face level air. Each vent assembly
incorporates a thumbwheel to regulate flow and moveable vanes to control direction.

HEATING AND VENTILATION

80-8

DESCRIPTION AND OPERATION

Control panel

The controls for heating and ventilation are installed on a control panel in the centre of the fascia, below the radio.
Three rotary knobs control the LH and RH outlet temperatures and distribution. A slider switch controls blower speed.
A latching pushswitch controls the selection of fresh/recirculated air; an amber LED in the switch illuminates when
recirculated air is selected.

Graphics on the panel and the controls indicate the function and operating positions of the controls.

Outlet vent
The outlet vent promotes the free flow of heating and ventilation air through the cabin. The outlet vent is installed in
the RH rear quarter body panel and vents cabin air into the sheltered area between the rear quarter body panel and
the outer body side panel. The vent consists of a grille covered by soft rubber flaps and is effectively a non-return
valve. The flap opens and closes automatically depending on the differential between cabin and outside air pressures.

FBH system (diesel models only)
The FBH system is an auxiliary heating system that compensates for the relatively low coolant temperatures inherent
in the diesel engine. At low ambient temperatures, the FBH system heats the coolant supply to the heater assembly,
and maintains it within the temperature range required for good in-car heating performance. Operation is fully
automatic, with no intervention required by the driver.

The system consists of an air temperature sensor, a FBH fuel pump and a FBH unit. Fuel for the FBH system is taken
from the fuel tank, through a line attached to the fuel tank's fuel pump, and supplied via the FBH fuel pump to the FBH
unit. The connection on the fuel tank's fuel pump incorporates a tube which extends down into the tank. At the FBH
unit connection, the fuel line incorporates a self-sealing, quick disconnect coupling. In the FBH unit, the fuel delivered
by the FBH fuel pump is burned and the resultant heat output is used to heat the coolant. An ECU integrated into the
FBH unit controls the operation of the system at one of two heat output levels, 2.5 kW at part load and 5 kW at full load

Ambient temperature sensor
The ambient temperature sensor controls a power supply from the alternator to the FBH unit. The sensor is installed
on the RH support strut of the bonnet closing panel and contains a temperature sensitive switch that is closed at
temperatures below 5

°

C (41

°

F) and open at temperatures of 5

°

C (41

°

F) and above.

HEATING AND VENTILATION

DESCRIPTION AND OPERATION

80-9

FBH fuel pump
The FBH fuel pump regulates the fuel supply to the FBH unit. The FBH fuel pump is installed in a rubber mounting on
the chassis crossmember immediately in front of the fuel tank. The pump is a self priming, solenoid operated plunger
pump, with a fixed displacement of 0.063 ml/Hz. The ECU in the FBH unit outputs a pulse width modulated signal to
control the operation of the pump. When the pump is de-energised, it provides a positive shut-off of the fuel supply to
the FBH unit.

FBH fuel pump nominal operating speeds/outputs

Sectioned view of FBH fuel pump

1 Solenoid coil
2 Plunger
3 Filter insert
4 Fuel line connector
5 'O' ring seal

6 Spring
7 Piston
8 Bush
9 Fuel line connector

10 Non return valve

The solenoid coil of the FBH fuel pump is installed around a housing which contains a plunger and piston. The piston
locates in a bush, and a spring is installed on the piston between the bush and the plunger. A filter insert and a fuel
line connector are installed in the inlet end of the housing. A non return valve and a fuel line connector are installed
in the fuel outlet end of the housing.

While the solenoid coil is de-energised, the spring holds the piston and plunger in the 'closed' position at the inlet end
of the housing. An 'O' ring seal on the plunger provides a fuel tight seal between the plunger and the filter insert,
preventing any flow through the pump. When the solenoid coil is energised, the piston and plunger move towards the
outlet end of the housing, until the plunger contacts the bush, and draw fuel in through the inlet connection and filter.
The initial movement of the piston also closes transverse drillings in the bush and isolates the pumping chamber at
the outlet end of the housing. Subsequent movement of the piston then forces fuel from the pumping chamber through
the non return valve and into the line to the FBH unit. When the solenoid coil de-energises, the spring moves the piston
and plunger back towards the closed position. As the piston and plunger move towards the closed position, fuel flows
passed the plunger and through the annular gaps and transverse holes in the bush to replenish the pumping chamber.

Operating phase

Speed, Hz

Output, l/h (US galls/h)

Start sequence

0.70

0.159 (0.042)

Part load

1.35

0.306 (0.081)

Full load

2.70

0.612 (0.163)

HEATING AND VENTILATION

80-10

DESCRIPTION AND OPERATION

FBH unit

1 Air inlet hose
2 Electrical connectors
3 Exhaust pipe
4 Quick disconnect coupling

5 Coolant inlet hose
6 Fuel supply line
7 Circulation pump
8 Coolant outlet hose

The FBH unit is installed on the bulkhead in the engine compartment, on the side opposite the brake servo, and is
connected in series in the coolant supply to the heater assembly. Two electrical connectors on the top of the FBH unit
connect to the vehicle wiring.

FBH unit connector pin details

Connector/Pin

No.

Description

Input/Output

C0925

2

K line (diagnostics)

Input/Output

3

Alternator power supply

Input

6

FBH fuel pump

Output

C0926

1

Battery power supply

Input

2

Earth

-