LAND ROVER DISCOVERY 1999 Workshop Manual

HEATING AND VENTILATION
80-4DESCRIPTION AND OPERATION
Air inlet duct
RH drive shown, LH drive similar
1Air outlet
2Resistor pack
3Wiring harness
4Blower
5Blower relay6Recirculated air servo motor
7Control flap operating mechanism
8Recirculated air inlet
9Recirculated air inlet
10Fresh air inlet
The air inlet duct is installed behind the fascia, on the passenger's side. The air inlet duct is connected to the plenum
to provide the fresh air inlet. Two grilles in the air inlet duct provide recirculated air inlets from the cabin. Two control
flaps, operated by a servo motor, open and close the fresh and recirculated air inlets to control the source of incoming
air. Operation of the servo motor is controlled by a switch on the control panel.
The blower is installed between the air inlets and the outlet to the heater assembly, and consists of an open hub,
centrifugal fan powered by an electric motor. Operation of the blower is controlled by a slider switch on the control
panel, via a blower relay mounted on the air inlet duct and a resistor pack. The resistor pack is installed in the air outlet
from the blower fan, so that any heat generated is dissipated by the air flow. A wiring harness on the air inlet duct
connects the servo motor, blower motor, blower relay and resistor pack to the vehicle wiring.

HEATING AND VENTILATION
DESCRIPTION AND OPERATION 80-5
Heater assembly
1Windscreen and side window air outlet
2Face level air outlet
3Casing
4Rear footwell air outlet
5Front footwell air outlet
6Drain outlet
7Air inlet8Engine coolant return
9Engine coolant feed
10Heater matrix
11RH temperature control cable
12Distribution control cable
13LH temperature control cable
The heater assembly heats and distributes air as directed by selections made on the control panel. The assembly is
installed on the vehicle centre-line, between the fascia and the engine bulkhead. The heater assembly consists of a
casing, formed from a series of plastic moldings, which contains a heater matrix and control flaps. Internal passages
integrated into the casing guide the air through the casing and separate it into two flows, one for the LH outlets and
one for the RH outlets. Two drain outlets at the bottom of the casing connect to overboard drain tubes installed in the
sides of the transmission tunnel.
Heater matrix
The heater matrix provides the heat source to warm the air being supplied to the distribution outlets. The heater matrix
is an aluminium two pass, fin and tube heat exchanger, installed in the RH side of the casing. Two aluminium tubes
attached to the heater matrix extend through the engine bulkhead to connect the heater assembly to the engine
coolant system. When the engine is running, coolant is constantly circulated through the heater matrix by the engine
coolant pump. On diesel models, the coolant flow is assisted by an electric pump while the FBH system is active.

HEATING AND VENTILATION
80-6DESCRIPTION AND OPERATION
Control flaps
Control flaps are installed in the heater assembly to control the temperature and distribution of air. Blend flaps control
the temperature and distribution flaps control the distribution.
Temperature and distribution control
Figure shows flaps set for medium heat to face level and footwell outlets
1Windscreen/Side windows outlet
2Heater assembly casing
3Air inlet
4Heater matrix5Front footwells outlet
6Rear footwells outlet
7Face level outlet
Blend flaps:Two sets of three blend flaps, one LH and one RH, regulate the flow of air through the heater matrix and
a heater matrix bypass, to control the temperature of the air leaving the heater assembly. The two sets of blend flaps
operate independently to allow different temperatures to be set for the LH and RH outlets.
Each blend flap is attached to a spindle. The end of each spindle extends through the side of the heater casing and
is attached to a common lever mechanism on the related side of the casing. A control cable is installed between the
lever mechanism and the related temperature knob on the control panel. When the flow is split between the bypass
and the heater matrix, the two flows mix downstream of the heater matrix to produce an even air temperature at the
individual outlets.
Distribution flaps: Separate distribution flaps are installed to control the flow of air to the footwells, windscreen/side
windows and the LH and RH face level outlets. The distribution flaps are attached to spindles that extend through the
RH side of the heater casing and are attached to a common lever mechanism. A control cable is installed between
the lever mechanism and the distribution knob on the control panel.

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
80-8DESCRIPTION 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
1Solenoid coil
2Plunger
3Filter insert
4Fuel line connector
5'O' ring seal6Spring
7Piston
8Bush
9Fuel line connector
10Non 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
80-10DESCRIPTION AND OPERATION
FBH unit
1Air inlet hose
2Electrical connectors
3Exhaust pipe
4Quick disconnect coupling5Coolant inlet hose
6Fuel supply line
7Circulation pump
8Coolant 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
2Earth -

HEATING AND VENTILATION
DESCRIPTION AND OPERATION 80-11
Sectioned view of FBH unit
1Combustion air fan
2Burner housing
3ECU
4Heat exchanger
5Burner insert
6Exhaust
7Glow plug/flame sensor8Evaporator
9Coolant inlet
10Circulation pump
11Fuel inlet
12Coolant outlet
13Air inlet
The FBH unit consists of:
lA circulation pump.
lA combustion air fan.
lA burner housing.
lAn ECU/heat exchanger.
lAn air inlet hose.
lAn exhaust pipe.
Circulation pump. The circulation pump is installed at the coolant inlet to the FBH unit to assist the coolant flow through
the FBH unit and the heater assembly. The pump runs continuously while the FBH unit is in standby or active
operating modes. While the FBH unit is inactive, coolant flow is reliant on the engine coolant pump.
Combustion air fan. The combustion air fan regulates the flow of air into the unit to support combustion of the fuel
supplied by the FBH pump. It also supplies the air required to purge and cool the FBH unit. Ambient air is supplied to
the combustion air fan through an air inlet hose containing a sound deadening foam ring.

HEATING AND VENTILATION
80-12DESCRIPTION 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.

HEATING AND VENTILATION
DESCRIPTION AND OPERATION 80-13
Operation
Air distribution
Turning the distribution knob on the control panel turns the control flaps in the heater assembly to direct air to the
corresponding fascia and footwell outlets.
Air temperature
Turning the LH or RH temperature knob on the control panel turns the related blend flaps in the heater assembly. The
blend flaps vary the proportion of air going through the cold air bypass and the heater matrix. The proportion varies,
between full bypass no heat and no bypass full heat, to correspond with the position of the temperature knob.
Blower speed
The blower can be selected off or to run at one of four speeds. While the ignition is on, when the blower switch is set
to positions 1, 2, 3, or 4, ignition power energises the blower relay, which supplies battery power to the blower. At
switch positions 1, 2 and 3, the blower switch also connects the blower to different earth paths through the resistor
pack, to produce corresponding differences of blower operating voltage and speed. At position 4, the blower switch
connects an earth direct to the blower, bypassing the resistor pack, and full battery voltage drives the blower at
maximum speed.
Fresh/Recirculated inlet air
When the recirculated air switch is latched in, the amber indicator LED in the switch illuminates and an earth is
connected to the recirculated air side of the fresh/recirculated air servo motor. The fresh/recirculated air servo motor
then turns the control flaps in the air inlet duct to close the fresh air inlet and open the recirculated air inlets.
When the latch of the recirculated air switch is released, the amber indicator LED in the switch extinguishes and the
earth is switched from the recirculated air side to the fresh air side of the fresh/recirculated air servo motor. The fresh/
recirculated air servo motor then turns the control flaps in the air inlet duct to open the fresh air inlet and close the
recirculated air inlets.
FBH system (where fitted)
The FBH system operates only while the engine is running and the ambient temperature is less than 5 °C (41 °F).
With the engine running and the ambient temperature below 5 °C (41 °F), the air temperature sensor connects the
alternator power supply to the ECU in the FBH unit. On receipt of the alternator power supply, the ECU starts the
circulation pump and, depending on the input from the temperature sensor in the heat exchanger, enters either a
standby or active mode of operation. If the heat exchanger casing temperature is 65 °C (149 °F) or above, the ECU
enters a standby mode of operation. If the heat exchanger casing temperature is below 65 °C (149 °F), the ECU enters
an active mode of operation. In the standby mode, the ECU monitors the heat exchanger casing temperature and
enters the active mode if it drops below 65 °C (149 °F). In the active mode, the ECU initiates a start sequence and
then operates the system at full or part load combustion to provide the required heat input to the coolant.
Start sequence
At the beginning of the start sequence the ECU energises the glow plug function of the glow plug/flame sensor, to
preheat the combustion chamber, and starts the combustion air fan at slow speed. After 30 seconds, the ECU
energises the FBH fuel pump at the starting sequence speed. The fuel delivered by the FBH fuel pump evaporates in
the combustion chamber, mixes with air from the combustion air fan and is ignited by the glow plug/flame sensor. The
ECU then progressively increases the speed of the FBH fuel pump and the combustion air fan to either part or full
load speed, as required by the system. Once full or part load speed is achieved, the ECU switches the glow plug/flame
sensor from the glow plug function to the flame sensing function to monitor combustion. From the beginning of the
start sequence to stable combustion takes approximately 90 seconds for a start to part load combustion and 150
seconds for a start to full load combustion.