1999 LAND ROVER DISCOVERY engine coolant

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.

HEATING AND VENTILATION
80-14DESCRIPTION AND OPERATION
Coolant temperature control
When the ECU first enters the active mode, it initiates a start to full load combustion. Full load combustion continues
until the heat exchanger casing temperature reaches 60 °C (140 °F), when the ECU decreases the speed of the FBH
fuel pump and the combustion air fan to half speed, to produce part load combustion. The ECU maintains part load
combustion while the heat exchanger casing temperature remains between 54 and 65 °C (129 and 149 °F). If the heat
exchanger casing temperature decreases to 54 °C (129 °F), the ECU switches the system to full load combustion
again. If the heat exchanger casing temperature increases to 65 °C (149 °F), the ECU enters a control idle phase of
operation.
On entering the control idle phase, the ECU immediately switches the FBH fuel pump off, to stop combustion, and
starts a timer for the combustion air fan. After a 2 minute cooldown period, the ECU switches the combustion air fan
off and then remains in the control idle phase while the heat exchanger casing temperature remains above 59 °C (138
°F). If the heat exchanger casing temperature decreases to 59 °C (138 °F), within 15 minutes of the ECU entering the
control idle phase, the ECU initiates a start to part load combustion. If more than 15 minutes elapse before the heat
exchanger casing temperature decreases to 59 °C (138 °F), the ECU initiates a start to full load combustion.
In order to limit the build-up of carbon deposits on the glow plug/flame sensor, the ECU also enters the control idle
phase if the continuous part and/or full load combustion time exceeds 72 minutes. After the cooldown period, if the
heat exchanger casing is still in the temperature range that requires additional heat, the ECU initiates an immediate
restart to part or full load combustion, as appropriate.
Shutdown
The FBH system is de-activated when the alternator power supply to the FBH unit is disconnected, either by the
engine stopping or, if the ambient temperature increases to 5 °C (41 °F) or above, by the contacts in the air
temperature sensor opening. If the system is active when the alternator power supply is disconnected, the ECU de-
energises the FBH fuel pump to stop combustion, but continues operation of the combustion air fan and the circulation
pump to cool down the FBH unit. The cool down time depends on the combustion load at the time the alternator power
input is disconnected.
Cool down times
Diagnostics
The ECU in the FBH unit monitors the system for faults. Any faults detected are stored in a volatile memory in the the
ECU, which can be interrogated by Testbook. A maximum of three faults and associated freeze frame data can be
stored at any one time. If a further fault is detected, the oldest fault is overwritten by the new fault.
The ECU also incorporates an error lockout mode of operation that inhibits system operation to prevent serious faults
from causing further damage to the system. In the error lockout mode, the ECU immediately stops the FBH fuel pump,
and stops the combustion air fan and circulation pump after a cool down time of approximately 2 minutes. Error lockout
occurs for start sequence failures and/or combustion flameouts, heat exchanger casing overheat and out of limit input
voltage. The error lockout mode can be cleared using Testbook, or by disconnecting the battery power supply for a
minimum of 10 seconds.
Start failure/flameout. If a start sequence fails to establish combustion, or a flameout occurs after combustion is
established, the ECU immediately initiates another start sequence. The start failure or flameout is also recorded by
an event timer in the ECU. The event timer is increased by one after each start failure or flameout, and decreased by
one if a subsequent start is successful. If the event timer increases to three (over any number of drive cycles), the
ECU enters the error lockout mode.
Heat exchanger casing overheat. To protect the system from excessive temperatures, the ECU enters the error
lockout mode if the heat exchanger casing temperature exceeds 105 °C (221 °F).
Out of limit voltage. The ECU enters the error lockout mode if the battery or alternator power input is less than 10.5 ±
0.3 V for more than 20 seconds, or more than 15.5 ± 0.5 V for more than 6 seconds.
Combustion load Cool down time, seconds
Part 100
Full 175

HEATING AND VENTILATION
80-22REPAIRS
Heater assembly - models without air
conditioning
$% 80.20.01.99
Remove
1.Drain cooling system.
l

+ COOLING SYSTEM - Td5,
ADJUSTMENTS, Drain and refill.
l

+ COOLING SYSTEM - V8,
ADJUSTMENTS, Drain and refill.
2. Diesel models: Remove 3 bolts and remove
engine cover.
3.Release clips and disconnect coolant hoses
from heater pipes.
CAUTION: Always fit plugs to open
connections to prevent contamination.
4.Remove facia assembly.

+ INTERIOR TRIM COMPONENTS,
REPAIRS, Fascia.5.Disconnect harness multiplug from heater
blower motor.
6.Remove bolt and 2 nuts securing heater
blower housing assembly to body and remove
blower.
7.Disconnect 2 drain tubes from base of heater.

HEATING AND VENTILATION
REPAIRS 80-23
8.Remove 2 screws securing console bracket to
tunnel and remove bracket.
9.Release radio coaxial cable from behind heater
pipes.
10.Protect the carpet from coolant spillage.
11.Remove 4 nuts and 1 bolt securing heater to
body.
12.Remove heater from vehicle.
13.Remove 2 screws securing heater RH and LH
footwell outlet duct to heater casing and
remove ducts. 14.Remove 2 screws securing matrix pipe bracket
to heater casing.
15.Remove screw securing pipe clamp to heater
casing and remove clamp.
16.Carefully remove matrix from heater.
Refit
1.Fit matrix into heater casing.
2.Fit screws securing pipe bracket to heater
casing.
3.Fit pipe clamp and secure with screw.
4.Fit heater ducts and secure with screws.
5.Position heater assembly to vehicle, ensure
heater coolant pipe grommet is correctly
located in bulkhead and secure with nuts and
bolt.
6.Fit radio coaxial cable behind heater pipes.
7.Fit console bracket and secure with screws.
8.Connect drain tubes to base of heater.
9.Fit blower unit to heater and secure to body
with nuts and bolt.
10.Connect harness multiplug to blower motor.
11.Fit facia assembly

+ INTERIOR TRIM COMPONENTS,
REPAIRS, Fascia.
12.Connect heater hoses and secure with clips.
13. Diesel models: Fit engine cover and secure
with bolts.
14.Refill cooling system
l

+ COOLING SYSTEM - Td5,
ADJUSTMENTS, Drain and refill.
l

+ COOLING SYSTEM - V8,
ADJUSTMENTS, Drain and refill.

HEATING AND VENTILATION
80-30REPAIRS
Pipe - Heater - Return
$% 80.25.12
Remove
1.Drain engine coolant.

+ COOLING SYSTEM - V8,
ADJUSTMENTS, Drain and refill.
2.Release clip securing heater return hose to
heater return pipe and disconnect hose from
pipe.
3.Remove bolt securing heater return pipe to
heater feed pipe.
4.Release clips securing engine harness and
vacuum pipe to heater return pipe.
5.Remove bolt securing heater return pipe to
cylinder head.
6.Release clip securing engine coolant hose to
heater return pipe.
7.Release engine coolant hose from heater
return pipe and collect pipe.Refit
1.Connect engine coolant hose to heater return
pipe and secure with clip.
2.Position heater return pipe to cylinder block and
secure with bolt.
3.Secure engine harness and vacuum pipe to
heater return pipe and secure with clips.
4.Fit and tighten bolt securing heater return pipe
to heater feed pipe.
5.Connect heater return hose to heater return
pipe and secure with clip.
6.Refill engine coolant.

+ COOLING SYSTEM - V8,
ADJUSTMENTS, Drain and refill.
M80 0437
M80 0438
4
46
7
5

AIR CONDITIONING
82-16DESCRIPTION AND OPERATION
Operation
General
While the system is on, the ATC ECU operates the refrigerant system and the inlet air, blower speed, air temperature
and air distribution functions to produce the conditions requested on the control panel. When the system is first
switched on, the ATC ECU resumes the control outputs in use when the system was last switched off. If conditions
have changed, or a different mode is selected to switch the system on, the control outputs are then changed to
produce the required new settings.
The system operates in automatic, economy and defrost modes, with manual overrides of the inlet air source, blower
speed and air distribution. The air temperature is automatically controlled in all operating modes.
In the automatic mode, the ATC ECU operates the system to warm-up or cool down the cabin to establish and
maintain the temperature selections on the control panel, while directing the air to those outlets most comfortable for
the occupant(s). If a difference between the LH and RH temperature selections causes a conflict of the required inlet
air source, blower speed or air distribution settings, priority is given to achieving the temperature requested on the
driver's side of the control panel.
The ATC ECU enters the economy mode when the refrigerant compressor is selected off while the system is in the
automatic mode, which reduces the load on the engine. Economy mode operation is similar to the automatic mode,
but without the ability to cool the cabin if the ambient temperature is higher than the temperature selections made on
the control panel, or to dehumidify the air in the cabin.
In the defrost mode, the ATC ECU sets the inlet air source to fresh air, the blower to maximum speed, the air
distribution to windscreen and side windows, and outputs signals to the BCU to operate the rear window heater and
(where fitted) the windscreen heater. The BCU starts or, if the heaters are already on, resets the heater timers and
energises the rear window and windscreen heaters for a complete on cycle.
Air temperature control
To determine the amount of heat or cooling required by the cabin, the ATC ECU uses the sensor inputs and the
temperatures selected on the control panel to calculate target air outlet temperatures for the driver's and the front
passenger's side of the heater assembly. The ATC ECU then signals the servo motors controlling the respective blend
flaps in the heater assembly to move to the flaps to the appropriate position. The target temperatures are constantly
updated and, in the automatic mode, also used in further calculations to determine the inlet air source, the blower
speed and the air distribution.
Inlet air control
The inlet air source is automatically controlled while the system is off or on. While the system is on, the inlet air source
can also be manually controlled to give timed recirculated air or latched recirculated air.
While the system is off, the ATC ECU uses vehicle speed to determine the inlet air source. With the vehicle at rest,
the inlet air source is set to recirculated air. When vehicle speed reaches 17.5 mph (28 km/h), the inlet air source
changes to fresh air. The inlet air source then remains at fresh air until the vehicle speed decreases to 5 mph (8 km/
h), when it returns to recirculated air.
While the system is on, the ATC ECU uses the LH and RH temperature selections, vehicle speed, ambient air
temperature and coolant temperature to determine the inlet air source. In the automatic mode:
lIf one temperature selection is set to LO and one is set to a specific temperature or HI, the inlet air is set to
recirculated air.
lIf one temperature selection is set to HI and one is set to a specific temperature or HI, the inlet air is set to fresh
air.
lWhen specific LH and RH temperature selections are set, the inlet air source remains at fresh air except when
the air distribution function is set to face level only or face level and footwell outlets. If the air distribution function
is set to face level only or face level and footwell outlets, at 56 mph (90 km/h) the inlet air source changes to
recirculated air (to exclude ram effect, which becomes excessive at speed). When the vehicle speed decreases
to 37.5 mph (60 km/h), the inlet air source returns to fresh air.
In the defrost mode, the inlet air source is set to fresh air except at low ambient air and coolant temperatures. If, within
5 minutes of the ignition being switched on, the vehicle speed is less than 5 mph (8 km/h) while the external air
temperature is −16 °C (3 °F) or less and the heater coolant temperature is −10 °C (14 °F) or less, then the inlet air
source is automatically set to the timed recirculated air mode. The timed recirculated air mode is cancelled
immediately the vehicle speed reaches 8 km/h or more .

AIR CONDITIONING
REPAIRS 82-29
REPAIRS
Compressor - diesel
$% 82.10.20
Remove
1.Remove engine acoustic cover.
2.Depressurise air conditioning system.

+ AIR CONDITIONING, REFRIGERANT
RECOVERY, RECYCLING AND
RECHARGING, Refrigerant recovery,
recycling and recharging.
3.Remove auxiliary drive belt.

+ CHARGING AND STARTING,
REPAIRS, Belt - auxiliary drive.
4.Drain cooling system.

+ COOLING SYSTEM - Td5,
ADJUSTMENTS, Drain and refill.
5.Disconnect multiplug from compressor.
6.Remove 2 bolts securing air conditioning pipes
to compressor and discard 'O' rings.
CAUTION: Always fit plugs to open
connections to prevent contamination.
7.Release clips and disconnect top hose from
coolant elbow and heater pipe.
8.Remove 4 bolts securing compressor to
mounting bracket.
9.Remove compressor.Refit
1.Calculate the quantity of refrigerant oil required.

+ GENERAL INFORMATION, Air
Conditioning Compressor Replacement.
2.Position compressor to mounting bracket and
tighten bolts to 25 Nm (18 lbf.ft).
3.Remove caps from compressor and pipe
connections.
4.Clean compressor and pipe connections.
5.Lubricate new 'O'rings with refrigerant oil and
fit to compressor.
6.Position A/C pipes to compressor and tighten
bolts to 10 Nm (7 lbf.ft) .
7.Connect multiplug to compressor.
8.Position top hose and secure with clips.
9.Refill cooling system.

+ COOLING SYSTEM - Td5,
ADJUSTMENTS, Drain and refill.
10.Fit auxiliary drive belt.

+ CHARGING AND STARTING,
REPAIRS, Belt - auxiliary drive.
11.Recharge air conditioning system.

+ AIR CONDITIONING, REFRIGERANT
RECOVERY, RECYCLING AND
RECHARGING, Refrigerant recovery,
recycling and recharging.
12.Fit engine acoustic cover.