Land Rover Discovery 99my To 03my Electrical Library 3rd Edition Rover Manual

							DESCRIPTION AND OPERATION
4.80DISCOVERY SERIES II
Power relay
The coil of the power relay receives a feed from fuse 31 in the passenger compartment 
fusebox. The feed passes on a GK wire to splice joint A9/A144. From the splice joint the feed 
passes on a GR wire to connector interface C0765-1/C0778-1. From the connector interface 
the feed passes, via splice joint A1, to the coil of the power relay. The coil is connected to 
pin C0793-10 on the ATC ECU.
The power relay operates speed 31 of the blower motor. This fastest motor speed is 
operated by the ATC ECU granting the earth path for the power relay coil. The energised 
coil closes the relay contacts and allows the earth for the front blower motor to pass, via 
splice joint A10, through the contacts. The earth path is completed on a B wire, via splice 
joints A9 and B9, to earth eyelet connector C0910-1.
Power transistor
The power transistor controls speeds 1 to 30 of the front blower motor. The power transistor 
is controlled by the ATC ECU on a PG wire to ECU pin C0792-8 and on a G wire to ECU pin 
C0793-1.
Speeds 1 to 30 are controlled by the power transistor varying the resistance to the earth flow 
from the front blower motor. The earth path from the front blower motor is connected on a B 
wire, via splice joint A10, to the power transistor. The power transistor is connected on a B 
wire, via splice joints A9 and B9, to earth eyelet connector C0910-1.
Air Temperature Control (ATC) ECU
The ATC ECU is connected from ECU pin C0792-2 to the SLABS ECU pin C0504-3 on a 
KG wire via header C0290. The SLABS ECU provides a speed signal to the ATC ECU for 
blower speed control.
On V8 engine vehicles, the ECM is connected on a PW wire to ATC ECU pin C0793-12.
On Td5 engine vehicles, the ECM is connected on a GO wire to ATC ECU pin C0793-9.
On all vehicles, the ATC ECU is connected from pin C0791-4 on a B wire, via header C0725, 
to earth header C0017 LHD/C0018 RHD.
Air conditioning (A/C) dual cut-off switch
The A/C dual cut-off switch is a high/low pressure switch fitted into the A/C system. When 
the switch is operated, the ECM signals the ATC ECU to request the air conditioning 
compressor clutch relay to be de-energised.
The ATC ECU is connected from ECU pin C0793-11 on a YB wire to the A/C dual cut-off 
switch. The A/C dual cut-off switch is connected on a YS wire, via header C0290 (LHD only), 
to the ECM. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.81
In-car temperature sensor
The in-car temperature sensor receives a feed from fuse 31 in the passenger compartment 
fusebox. The feed passes on a GK wire to splice joint A9/A144. From the splice joint the feed 
passes on a GR wire to the in-car temperature sensor and is connected to a motor which 
draws air over the sensor. The motor is connected on a B wire from the in-car temperature 
sensor, via header C0760, to earth header C0017 LHD/C0018 RHD.
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joint A145/A146 to the in-car temperature sensor. An input from the sensor is connected on 
a WB wire to the ATC ECU pin C0792-7.
Ambient Air Temperature (AAT) Sensor
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joint A145/A146 to the AAT sensor. An input from the sensor is connected on a YG wire to 
the ATC ECU pin C0792-6.
Heater Coolant Temperature (HCT) Sensor
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joints A145/A146, A26, B26, C26 and D26 to the HCT sensor. An input from the sensor is 
connected on an RB wire to the ATC ECU pin C0792-5.
Evaporator sensor
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joints A145/A146, A26, B26, C26 and D26 to the evaporator sensor. An input from the 
sensor is connected on a PB wire to the ATC ECU pin C0792-18.
Sunlight sensor
A reference voltage from the ATC ECU pin C0791-3 is connected on a GW wire, via splice 
joint A278, to the sunlight sensor. Two inputs from the sunlight sensor are connected on WU 
and WR wires to ATC ECU pins C0792-16 and C0792-17 respectively.
Air Temperature mode motor – LH
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joints A146/A146, A26 and B26 to the LH air temperature mode motor.
A reference voltage from the ATC ECU pin C0791-3 is connected on a GW wire to splice 
joint A278. From the splice joint the reference voltage continues on a GR wire, through splice 
joint A22 to the LH air temperature mode motor.
An input from the LH air temperature mode motor is passed to pin C0792-14 on the ATC 
ECU on an SU wire.
Two outputs from ATC ECU pins C0793-14 and C0793-6 are connected to the LH air 
temperature mode servo motor on GU and UO wires respectively. Each output drives the 
servo motor to blend hot or cold air. 
						

							DESCRIPTION AND OPERATION
4.82DISCOVERY SERIES II
Air temperature mode motor – RH
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joints A145/A145, A26, B26 and C26 to the RH air temperature mode motor.
A reference voltage from the ATC ECU pin C0791-3 is connected on a GW wire to splice 
joint A278. From the splice joint the reference voltage continues on a GR wire, through splice 
joint A22 and B22 to the RH air temperature mode motor.
An input from the RH air temperature mode motor is passed to pin C0792-15 on the ATC 
ECU on a YG wire.
Two outputs from ATC ECU pins C0793-13 and C0793-5 are connected to the RH air 
temperature mode servo motor on Y and PY wires respectively. Each output drives the servo 
motor to blend hot or cold air.
Air distribution mode motor
A reference voltage from the ATC ECU pin C0791-8 is connected on a BW wire, via splice 
joints A145/A146, and A26 to the air distribution mode motor.
A reference voltage from the ATC ECU pin C0791-3 is connected on a GW wire to splice 
joint A278. From the splice joint the reference voltage continues on a GR wire, through splice 
joint A22 and B22 to the air distribution mode motor.
An input from the air distribution mode motor is passed to pin C0792-4 on a UY wire.
Two outputs from ATC ECU pins C0793-15 and C0793-7 are connected to the air 
distribution servo motor on US and UW wires respectively. Each output drives the servo 
motor to the windscreen demist or footwells position.
Rear Air Conditioning Operation
Rear Blower relay
A feed from fusible link 4 in the engine compartment fusebox is connected by an NK wire to 
the passenger compartment fusebox. The feed passes through fuse 6 in the the passenger 
compartment fusebox and is connected by a YG wire to the contacts of the rear blower relay.
A feed from fuse 31 in the passenger compartment fusebox is connected on a GK wire, via 
header C0289 (RHD only), to connector interface C0692-4/C0856-4. From the connector 
interface the feed continues on a WG wire to diode (G126). From the diode the feed is 
connected on a U wire, through splice joint A48, to the coil of the rear blower relay.
The coil of the rear blower relay is connected on a PG wire to the rear air conditioning switch. 
The contacts of the rear blower relay are connected on a B wire to earth header C0707, via 
splice joint A52 when the relay coil is de-energised. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.83
When the rear air conditioning switch is operated, the rear blower relay coil is energised, 
closing the relay contacts. This allows the feed from fusible link 4 in the engine compartment 
fusebox to pass through the relay to operate the rear blower motor on an NR wire.
Rear air conditioning switch
When the rear A/C switch is operated, an earth path is completed from the switch on a BR 
wire to the rear blower switch. The completion of the earth path energises the coil of the rear 
blower relay and illuminates the switch ON illumination.
The completion of the earth path is also used by the ATC ECU to sense when rear A/C has 
been selected on. A PG wire is connected from the rear A/C switch, via splice joint A58, to 
ATC ECU pin C0792-13.
From splice joint A48, the feed from fuse 31 is also connected on a U wire to connector 
interface C0856-3/C0692-3. From the connector interface the feed is connected to the on/
off illumination of the rear air conditioning switch on a WG wire.
Rear blower motor
The rear blower motor is connected on a G wire to splice joint A44. From splice joint A44 the 
motor is connected on G wires to the rear blower switch and the resistor pack.
Rear blower switch
The rear blower switch is a four position switch which controls the speed of the rear blower 
motor through a resistor pack.
With the switch in position 1, the earth path for the rear blower motor cannot pass through 
the rear blower switch. The earth path is through a fusible link and three resistors in the 
resistor pack to earth header C0707 on a B wire. This causes the rear blower motor to 
operate at the slowest speed.
With the switch in position 2, the earth path for the rear blower motor is through the fusible 
link and two resistors in the resistor pack to the switch on an N wire. The switch is connected 
to earth header C0707 on a TB wire. This causes the rear blower motor to operate at the 
second slowest speed.
With the switch in position 3, the earth path for the rear blower motor is through the fusible 
link and one resistor in the resistor pack to the switch on a Y wire. The switch is connected 
to earth header C0707 on a B wire. This causes the rear blower motor to operate at the 
second fastest speed.
With the switch in position 4, the earth path for the rear blower motor is direct to the rear 
blower switch on a G wire, by-passing the resistor pack. This allows full power to flow 
through the motor which operates at its fastest speed. 
						

							DESCRIPTION AND OPERATION
4.84DISCOVERY SERIES II
HEATER BLOWER - FRESH/RECIRCULATED AIR MOTOR (NON A/C 
VEHICLES)
DESCRIPTION
General
The heater blower is operated from a four position linear switch located in the centre of the 
fascia on the heater control panel. The blower motor only operates with the ignition switch 
in position II. The blower motor control switch is illuminated when the side lights are turned 
on.
The blower motor is located in the air inlet duct. A resistor pack is located on the air inlet duct 
and controls the voltage through the blower motor for fan speeds one, two and three. Fan 
speed four drives the blower motor at full speed with a 12 V direct supply through the motor. 
Position zero is the off position.
Fresh/Recirculated Air Description
The heater blower circuit also incorporates a fresh/recirculated air switch and motor. The 
latching fresh/recirculated air switch is located in the centre of the fascia and has an indicator 
light to show when the switch is in the recirculation position. The switch is illuminated when 
the side lights are turned on. The fresh/recirculated air motor only operates with the ignition 
switch in position II.
The switch is connected to the fresh/recirculated air mode motor which, when selected, 
moves a flap in the heater air distribution unit to prevent the intake of air from outside the 
vehicle. A warning lamp on the switch illuminates to show that recirculated air has been 
selected.
OPERATION
Heater Blower - Fresh/Recirculated Air Supply
Circuit supply
A feed from the battery positive terminal is connected by an R wire to the engine 
compartment fusebox, where it passes through fusible links 1, 4 and 8. Fusible links 1 and 
4 are connected in series.
The feed from fusible links 1 and 4 is connected from the engine compartment fusebox to 
the passenger compartment fusebox on an NK wire, where it passes through fuse 7. The 
feed is connected from the passenger compartment fusebox to the contacts of the blower 
relay on an NR wire.
A feed from fusible link 8 in the engine compartment fusebox is connected on an NW wire 
to the passenger compartment fusebox and from the fusebox to the ignition switch on an N 
wire. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.85
Ignition switch supply
When the ignition switch is in position II, the feed from fusible link 8 flows through the ignition 
switch to the passenger compartment fusebox on a W wire where it passes through fuse 31. 
From fuse 31 the feed is connected on a GK wire to splice joint A240.
From the splice joint A240 the feed is connected on a GK wire to the fresh recirculated air 
switch.
From the splice joint A240, the feed is also connected on a GR to splice joint A5. From the 
splice joint A5 the feed is connected on GR wires to the coil of the blower relay and the fresh/
recirculated air mode motor.
Heater Blower Operation
The speed of the front blower motor is controlled by the blower motor switch position and 
three resistors located in the resistor pack. The blower motor will only operate with the 
ignition switch in position II.
With the ignition switch in position II and the blower motor switch in position 0 (off), the earth 
path for the blower relay coil is not complete and the relay coil cannot energise.
When the blower motor switch is moved to position 1, 2, 3 or 4 the blower relay coil is 
connected to earth on an N wire to the blower motor switch. The blower motor switch is 
connected on a B wire, via splice joint A7, to earth eyelet connector C0910-1. This causes 
the blower relay coil to energise closing the relay contacts.
With the relay contacts closed, the feed from fuse 7 in the passenger compartment fusebox 
passes through the relay contacts to the front blower motor.
With the blower motor switch in position 1, the earth path for the motor is via the resistor 
pack, through the 40 Amp in-line fuse and the three resistors (0.32/0.85/1.71 ohms) which 
limit the power flow to earth and operate the blower motor at slow speed. The resistor pack 
is connected on a B wire, via splice joint A7, to earth eyelet connector C0910-1.
With the blower motor in position 2, the earth path for the motor is via the resistor pack, 
through the in-line fuse and two resistors (0.32 and 0.85 ohms) which limit the power flow to 
earth and operate the blower motor at slow/medium speed. The resistor pack is connected 
on a PU wire to the blower motor switch. The blower motor switch is connected on a B wire, 
via splice joint A7, to earth eyelet connector C0910-1.
With the blower motor switch in position 3, the earth path for the blower motor is via the 
resistor pack, through the in-line fuse and through one resistor (0.32 ohm) which limits the 
power flow to earth and operates the blower motor at medium/fast speed. The resistor pack 
is connected on a G wire to the blower motor switch. The blower motor switch is connected 
on a B wire, via splice joint A7, to earth eyelet connector C0910-1. 
						

							DESCRIPTION AND OPERATION
4.86DISCOVERY SERIES II
With the blower motor switch in position 4, the earth path for the blower motor is direct to the 
blower motor switch on a BO wire via splice joint A1 and operates the blower motor at fast 
speed. The blower motor switch is connected on a B wire, via splice joint A7, to earth eyelet 
connector C0910-1.
Fresh/Recirculated Air Operation
The fresh/recirculated air mode motor can only operate when the ignition switch is in position 
II. The feed from fuse 31 in the passenger compartment fusebox is connected to the fresh/
recirculated air switch and the fresh/recirculated air mode motor.
Fresh air position
When the switch is in the fresh air position (latched out, indicator lamp off), the feed from 
fuse 31 on a GK wire cannot pass through the indicator bulb to earth due to the switch 
position.
The air mode motor is connected on an UB wire to the switch. When the motor reaches the 
end of its operation to move the fresh/recirculation air flap, an internal switch in the motor 
moves ready to accept a feed to move to the recirculate air position. While the motor is 
operating it is connected through the switch on a B wire, via headers C0725 and C0760 to 
earth header C0017 LHD/C0018 RHD.
Recirculated air position
When the switch is in the recirculate position (latched in, indicator lamp on) the feed from 
fuse 31 can pass through the indicator bulb which illuminates and flows through the switch 
contacts. The switch is connected on a B wire, via headers C0725 and C0760 to earth 
header C0017 LHD/C0018 RHD.
The air mode motor is connected on an RG wire to a diode and from the diode to the switch 
on an RU wire. When the motor reaches the end of its operation to move the fresh/
recirculation air flap, an internal switch in the motor moves ready to accept a feed to move 
to the fresh air position. While the motor is operating it is connected through the switch on a 
B wire, via headers C0725 and C0760 to earth header C0017 LHD/C0018 RHD. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.87
FUEL BURNING HEATER (FBH) - Td5 ONLY
DESCRIPTION
General
The FBH system is an optional auxiliary heating system that compensates for relatively low 
coolant temperatures inherent in Diesel engines. At low ambient temperatures, the FBH 
system heats the coolant supply to the heater matrix and maintains it at a temperature for 
good in-car heating performance. FBH operation is fully automatic with no driver intervention 
required.
The system comprises an air temperature sensor, FBH pump and the FBH unit. The FBH 
unit has diagnostic capabilities and can be interrogated by TestBook/T4.
OPERATION
FBH Supply
Circuit supply
A feed from the battery positive terminal is connected by an R wire to the engine 
compartment fusebox where it passes through fusible link 8 and fuse 9.
The feed from fusible link 8 is connected to the passenger compartment fusebox on an NW 
wire and from the fusebox to the ignition switch on an N wire.
Ignition switch supply
When the ignition switch is in position II, the feed from fusible link 8 flows through the ignition 
switch to the passenger compartment fusebox on a Y wire and passes through fuse 27.
FBH Operation
From fuse 27, the feed passes through header C0760 to the instrument pack on an LG wire. 
The feed passes through the ignition/no charge warning lamp and is connected, via header 
C0294 LHD/C0287 RHD to the alternator by a NY wire. With the engine not running, the feed 
from the ignition switch passes to earth through the alternator windings and illuminates the 
ignition/no charge warning lamp.
When the engine is running, the voltage produced by the alternator, passes on the NY wire 
to header C0294 LHD/C0287 RHD extinguishing the ignition/no charge warning lamp. 
Simultaneously, the feed from the alternator passes on a third NY wire from the header 
C0294 LHD/C0287 RHD to the FBH air temperature sensor.
At temperatures below 5 degrees C (41 degrees F), the sensor contacts are closed and 
connect the feed from the alternator to FBH unit, on an N wire from the sensor to header 
C0294 and an NY wire from header C0294 to the FBH unit. 
						

							DESCRIPTION AND OPERATION
4.88DISCOVERY SERIES II
A feed from fuse 9 in the engine compartment fusebox is connected on a PN wire to the FBH 
unit. When the FBH unit senses the voltage from the air temperature sensor, internal 
circuitry in the FBH unit allows the feed from fuse 9 to activate the FBH. The FBH unit is 
connected on a B wire to earth header C0018 LHD/C0017 RHD.
The FBH unit supplies a feed on a WU wire to the FBH pump. The feed operates the FBH 
pump which is connected on a B wire to earth eyelet connector C0810-1.
The FBH unit is connected on a R wire to the diagnostic socket. This allows the FBH to be 
interrogated by TestBook/T4 to retrieve FBH diagnostic information. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.89
COOLING FAN
DESCRIPTION
General
The cooling fan is located on brackets forward of the radiator. The fan motor is operated by 
a cooling fan relay controlled by the Engine Control Module (ECM). The main relay supplies 
a feed to the coil of the cooling fan relay. A permanent feed is supplied to the coils of the 
main and cooling fan relays located in the engine compartment fusebox. On V8 models a 
coolant temperature sensor is located in the inlet manifold, on Td5 models the sensor is 
located in the outlet housing.
The ECM controls the operation of the main and cooling fan relays. At a preset temperature 
the ECM receives an input from a coolant temperature sensor above the values stored in 
the ECM. The ECM logic enables the earth path for the coil of the cooling fan relay. The fan 
motor then gets a feed from the closed contacts of the cooling fan relay.
When the engine temperature falls, the sensor gives an input below the values stored in the 
ECM. When the input from the coolant temperature sensor is low, the ECM interrupts the 
earth path to the coil of the cooling fan relay. The contacts of the cooling fan relay open, this 
action breaks the feed to the cooling fan motor, and the motor stops. The cycle will start 
again when the engine coolant temperature rises and the sensor sends a high input to the 
ECM.
The ECM has an engine off function, when the ignition is turned off the ECM logic goes into 
a watchdog routine and monitors the coolant temperature for approximately seven to ten 
seconds. If the coolant temperature is still high, over 100 degrees C (212 degrees F) V8, 110 
degrees C (230 degrees F) Td5, the ECM logic can control the operation of the fan motor.
On V8 engines the ECM will only enable the fan if the inlet air temperature is over 60 degrees 
C (140 degrees F). The ECM will allow the fan to run for a maximum of ten minutes, however 
the ECM continues to monitor the coolant temperature. The ECM logic will stop the fan if the 
coolant temperature is below the acceptable values stored in the ECM. To prevent a flat 
battery, the fan will be stopped (regardless of coolant temperature) if the battery voltage falls 
to 12 V.