relay LAND ROVER DISCOVERY 1999 Repair Manual

AIR CONDITIONING
82-12DESCRIPTION AND OPERATION
Control panel
1LH temperature switch
2Economy mode (ECON) switch
3Blower switch
4Display
5Distribution switch
6External air temperature (EXT) switch7RH temperature switch
8Fresh/Recirculated air switch
9Defrost mode switch
10Automatic mode (AUTO) switch
11A/C on/off switch
14 Driver's blend flaps position Input
15 Passenger's blend flaps position Input
16 LH solar heating load Input
17 RH solar heating load Input
18 Evaporator Input
19 Not used -
20 Not used -
C0793
1 Blower power transistor base current Output
2 Blower relay Output
3 Windscreen heater request Output
4 Rear screen heater request Output
5 Passenger's blend flaps servo motor, drive to hot Output
6 Driver's blend flaps servo motor, drive to hot Output
7 Distribution flaps servo motor, drive to windscreen and side
windows demistOutput
8 Fresh/Recirculated air servo motor, drive to recirculated air Output
9 Cooling fan request (diesel models) Output
10 Power relay Output
11 Compressor clutch request Output
12 Cooling fan request (V8 models) Output
13 Passenger's blend flaps servo motor, drive to cold Output
14 Driver's blend flaps servo motor, drive to cold Output
15 Distribution flaps servo motor, drive to footwells Output
16 Fresh/Recirculated air servo motor, drive to fresh air Output Connector/Pin
No.Description Input/Output

AIR CONDITIONING
DESCRIPTION AND OPERATION 82-17
Timed recirculated air
The timed recirculated air mode sets the inlet air source to recirculated air for 5 ± 1 minutes, after which it automatically
reverts to fresh air. Timed recirculated air can be manually selected:
lIn the automatic mode, by pressing the fresh/recirculated air switch for 1.5 seconds or more; the audible warning
sounds twice.
lIn the economy or defrost modes, by pressing the fresh/recirculated air switch for less than 1.5 seconds; the
audible warning sounds once.
Latched recirculated air
The inlet air source can be latched to recirculated air:
lIn the automatic mode, by pressing the fresh/recirculated air switch for less than 1.5 seconds; the audible
warning sounds once.
lIn the economy or defrost modes, by pressing the fresh/recirculated air switch for 1.5 seconds or more; the
audible warning sounds twice.
Blower control
The ATC ECU operates a blower relay, power transistor and power relay to run the blower at one of 31 stepped
speeds. All speed steps are available in the automatic modes of blower control. In the manual mode, speed steps 3,
10, 16, 22 and 31 are used to provide slow, three intermediate and fast blower speeds. The ATC ECU energises the
blower relay and modulates the power transistor to operate the blower for speed steps 1 to 30. For speed step 31, the
ATC ECU energises the power relay, which switches the earth side of the blower motor direct to earth, bypassing the
power transistor.
In the automatic, economy and defrost modes, blower speed is corrected for vehicle speed to compensate for the
increase in ram effect on the inlet air as the vehicle speed increases. Correction begins at approximately 50 km/h,
when blower speed is progressively decreased as vehicle speed increases, until a maximum decrease of 13 steps
occurs at 123 km/h. Similarly, blower speed increases as vehicle speed decreases down to approximately 50 km/h.
In the automatic and economy modes, if the LH or RH temperature is set to LO or HI, the blower runs at maximum
speed with correction only for vehicle speed. If both the LH and RH outlet air temperatures are set to a specific
temperature, blower speed corrections are added to compensate for the heater coolant temperature, external air
temperature, and the solar load acting on the vehicle:
lDuring warm-up, the blower speed is set to 3 while the heater coolant temperature is below approximately 20 °C
(68 °F). From approximately 20 °C (68 °F), the blower speed is progressively increased as the coolant
temperature increases, until maximum speed is set at approximately 50 °C (122 °F).
lDuring cool down, blower speed is set to 3, for 5 seconds after the system is switched on. Over the following 6
seconds, the blower speed is progressively increased up to maximum speed.
lAs the temperature in the cabin approaches the selected temperatures, blower speed is progressively reduced
until, once the selected temperatures have been established, blower speed stabilises at approximately 6.
lSolar heating correction is employed when air distribution is set to face level or to face and footwells. The
correction progressively increases the blower speed, up to a maximum of 9 steps, with increasing values of solar
heating.

AIR CONDITIONING
82-18DESCRIPTION AND OPERATION
Air distribution control
To control the air distribution within the cabin the ATC ECU signals the servo motor controlling the distribution flaps
in the heater assembly to move to the flaps to the appropriate position.
In the automatic and economy modes, if the LH or RH temperature selections are set to LO or HI, air distribution is
fixed as follows:
lIf one is set to LO and one is set to a specific temperature, to face level only.
lIf one is set to HI and one is set to a specific temperature, to footwells only.
lIf one is set to LO and one is set to HI, to face level and footwells.
When specific LH and RH temperature selections are set, air distribution is determined from the target air outlet
temperatures. For higher target air outlet temperatures, air distribution is set to footwells only. For lower target air
outlet temperatures, air distribution is set to face level only. For intermediate target air outlet temperatures, air
distribution is set to face level and footwells. When the air distribution is set to face level and footwells, the ATC ECU
varies the bias between the footwells and the face level outlets, in three stages, to provide a gradual transition of air
distribution from footwells only to face level only. The three stages of bias are also employed when the air distribution
is manually selected to face level and footwells.
During warm-up, the air distribution changes to face level and footwells for a period, then reverts to footwells only.
The period of air distribution at face level and footwells can be cancelled by pressing and holding the on/off and defrost
mode switches, then turning the ignition switch from off to on. Pressing and holding the AUTO and defrost switches,
then turning the ignition switch from off to on, restores the period of air distribution at face level and footwells.
Compressor control
To engage the compressor clutch, the ATC ECU outputs a compressor clutch request to the ECM, which then
energises the A/C compressor clutch relay. Compressor operation is governed by the evaporator outlet air
temperature, at one of two settings, dependent on the amount of cooling required. When more cooling is required, the
compressor clutch request is output if evaporator outlet air temperature increases to 4 °C (39 °F) and cancelled when
it decreases to 3 °C (37 °F). When less cooling is required, the compressor clutch request is output if evaporator outlet
air temperature increases to 11 °C (52 °F) and cancelled when it decreases to 10 °C (50 °F).
Engine cooling fan control
While the A/C system is on, operation of the electric engine cooling fan, to assist refrigerant condenser operation, is
determined by a combination of vehicle speed and external air temperature. When cooling fan operation is required,
the ATC ECU outputs a cooling fan request to the ECM, which then energises the cooling fan relay. The cooling fan
request is output if vehicle speed is 80 km/h or less while the external air temperature is 28 °C (82 °F) or more. The
request is cancelled, and the cooling fan switched off, if either the vehicle speed increases to 100 km/h, or the external
air temperature decreases to 25 °C (77 °F).
Default settings
If the battery power supply to the ATC ECU is disrupted for any reason, e.g. battery disconnected, the system reverts
to default settings when the battery power supply is restored. Default settings are:
lTemperature indications in °C (in some markets a conversion connector is fitted to the ATC ECU to change the
default temperature scale to °F).
lLH and RH outlet temperatures of 22 °C (72 °F).
laudible warning switched on.
lWarm-up air distribution (to face level and footwells) function switched on.
lIf the system is first switched on using the A/C on/off switch, the automatic mode is engaged, regardless of the
settings in use when the battery was disconnected.

AIR CONDITIONING
82-24DESCRIPTION AND OPERATION
Rear evaporator/blower assembly
1Resistor pack
2Thermostatic expansion valve
3Rear blower relay
4Air outlet
5Evaporator6Capillary tube
7Housing
8Condensate drain outlet
9Refrigerant lines
10Blower
The rear evaporator/blower assembly cools and dehumidifies air from the cabin and supplies it to the rear distribution
system. The unit is installed on the left side of the loadspace, behind the quarter trim. A grille in the quarter trim allows
air to flow from the loadspace into the evaporator/blower. Refrigerant lines for the evaporator and a condensate drain
tube are attached to the rear floor.
The evaporator and blower are installed in a common housing, which also incorporates the resistor pack for the
blower. A thermostatic expansion valve is integrated into the inlet refrigerant line. A rear blower relay is attached to
the top of the housing.
Evaporator
The evaporator absorbs heat from the recirculated air being supplied to the distribution ducts.
Thermostatic expansion valve
The thermostatic expansion valve meters the flow of refrigerant into the evaporator to match the heat load of the air
passing through the evaporator matrix. A capillary tube, attached to the outlet pipe of the evaporator and connected
to the thermostatic expansion valve, automatically adjusts the valve opening in relation to the refrigerant temperature
at the evaporator outlet.

AIR CONDITIONING
DESCRIPTION AND OPERATION 82-25
Blower
The blower controls the volume of air being supplied to the distribution outlets. The blower is an open hub, centrifugal
fan powered by an electric motor. A dust filter is installed over the fan inlet. The blower switch on the control panel
and the resistor pack control the operation of the blower, which can be selected to run at one of four speeds.
Resistor pack
The resistor pack supplies reduced voltages to the blower motor for blower speeds 1, 2 and 3. For blower speed 4,
the resistor pack is bypassed and battery voltage drives the motor at full speed. The pack is installed in the air outlet
from the blower fan, so that any heat generated is dissipated by the air flow.
Distribution system
Air ducts
Ducts connected to the rear evaporator/blower motor assembly distribute air to five vent assemblies in the roof.
Vent assemblies
The vent assemblies allow occupants to control the flow and direction of air. Each vent assembly incorporates a
thumbwheel to regulate flow and moveable vanes to control direction.
Rear control system
The control system operates the blower to control the operation of the rear A/C. The control system consists of two
control switches and a rear blower relay.
Control switches
A rear A/C switch and a blower speed switch are installed on a control panel in the roof lining. The A/C switch is a
latching pushswitch with an amber indicator lamp which illuminates when rear A/C is selected on. The blower speed
switch is a slide switch with a positive detent at each of four speed positions (there is no off position).
Rear blower relay
The rear blower relay controls the electrical supply to the blower.

AIR CONDITIONING
82-26DESCRIPTION AND OPERATION
Operation
The rear A/C only operates if the front A/C is on to pump refrigerant through the rear evaporator/blower assembly.
When the rear A/C switch is selected on, the indicator lamp in the switch illuminates and the rear blower relay is
energised. The rear blower relay switches battery power to the blower motor, which runs at the speed selected on the
blower speed switch.
The air from the blower passes through the evaporator matrix, which absorbs heat from the air. The cooled air is then
supplied to the roof vents through the distribution ducts. The heat absorbed by the refrigerant in the evaporator is
sensed by the thermostatic expansion valve. The thermostatic expansion valve then opens and regulates the flow of
refrigerant through the evaporator in proportion to the amount of heat being absorbed from the air.
When the rear A/C switch is selected off, the blower stops. The thermostatic expansion valve senses the subsequent
decrease in temperature of the refrigerant in the evaporator. The thermostatic expansion valve then closes and stops
the flow of refrigerant, except for a minimal bleed flow.

AIR CONDITIONING
82-42REPAIRS
Evaporator - rear
$% 82.26.20
Remove
1.Remove evaporator assembly.

+ AIR CONDITIONING, REPAIRS,
Evaporator and motor assembly - rear.
2.Remove insulation from TXV.
3.Release relay from support bracket.
4.Remove ducting seal.
5.Remove 4 screws securing lower part of
casing, release and remove lower casing. 6.Remove 6 screws and 4 clips securing main
casing and remove top half of casing.
7.Loosen and release evaporator pipes unions,
release pipes and remove evaporator.
8.Remove and discard evaporator pipe 'O' rings.
Refit
1.Lubricate new 'O' rings with clean refrigerant oil
and fit to evaporator pipes
2.Position evaporator, connect pipes and tighten
unions.
3.Position main casing and secure with clips and
screws.
4.Position lower part of casing and secure with
screws.
5.Fit ducting seal
6.Secure relay to support bracket.
7.Fit insulation to TXV.
8.Fit evaporator assembly.

+ AIR CONDITIONING, REPAIRS,
Evaporator and motor assembly - rear.

WIPERS AND WASHERS
DESCRIPTION AND OPERATION 84-1
WIPERS AND WASHERS DESCRIPTION AND OPERAT ION
Wipers and washers component layout
RHD shown, LHD similar
1Headlamp power wash relay
2Passenger compartment fuse box
(rear wiper relay, front wiper relay and IDM)
3Variable Delay Switch
4Front wash/ wipe switch
5Rear wiper motor
6Rear washer switch7Rear wiper switch
8Body Control Unit (BCU)
9Front washer pump
10Rear washer pump
11Front wiper motor assembly
12Headlamp power wash pump

WIPERS AND WASHERS
DESCRIPTION AND OPERATION 84-7
1BCU
2IDM
3Front wiper relay
4Front wash / wipe switch
5Front wiper motor assembly
6Front washer pump motor
7Variable delay switch
8Rear wiper relay
9Rear wiper switch
10Rear washer switch
11Rear wiper motor
12Rear washer pump motor
13Headlamp power wash relay
14Headlamp power wash pump motor

WIPERS AND WASHERS
84-8 DESCRIPTION AND OPERATION
Description
General
All markets have a common wiper system with headlamp powerwash as an option.
The wipers system comprises two front wipers and one rear wiper which are powered by electric motors. A washer
reservoir is located in the front left hand wheel arch and is fitted with two electric pumps. Each pump supplies washer
fluid to either the front or rear screens. On certain models, a third pump can be fitted to operate a headlamp power
wash function. Operation of the front and rear wipers and washers is controlled by the driver using switches located
on a steering column stalk and push button switches on the fascia.
Control of the wipers and washers is achieved by the following components:
lBCU.
lIDM.
lFront wiper relay.
lFront wash/ wipe switch.
lVariable delay switch.
lFront wiper motor assembly.
lFront washer pump motor.
lRear wiper relay.
lRear wiper switch.
lRear washer switch.
lRear wiper motor.
lRear washer pump motor.
Both the Body Control Unit (BCU) and the Intelligent Driver Module (IDM) control the wiper system. The BCU controls
the time delay function of the wiper system and is located below and behind the passenger glovebox. During engine
cranking the BCU prevents wiper functions. Two relays are located in the passenger compartment fusebox. The
relays control the delay operation of the front and rear wipers. The relays are an integral part of the fusebox and
cannot be renewed separately.
Power for the wiper system is supplied by the IDM, which is integral with the passenger fusebox and cannot be
renewed as a component. A serial communication link allows communication between the IDM and the BCU.
The system has diagnostic capabilities through TestBook.
Front wipers
The two front windscreen wipers are operated by a linkage assembly and an electric motor located under the plenum
grill below the windscreen. The linkage and motor assembly is handed for left and right hand drive vehicles. The motor
is an integral part of the linkage and cannot be replaced separately.
The linkage comprises a pressed steel mounting plate which provides for the attachment of a wheel box at each end.
The mounting plate is secured to the bulkhead with flanged nuts which attach to a stud plate located behind the
bulkhead. A link arm is attached to each wheel box by a short link and secured with circlips. The link arm has an
attachment hole centrally located along its length for the electric motor drive link.
The electric motor is mounted in a recess in the bulkhead below a sealed cover plate. The drive spindle of the motor
protrudes through the cover plate and is fitted with a link. The link is attached to a tapered spline on the motor spindle
and is secured with a lock washer and nut. The opposite end of the link is attached to the central attachment point on
the link arm and secured with a circlip.
Each wheel box has a taper splined shaft which allows for the attachment of the wiper arm which is secured with a
washer and nut. The shaft of each wheel box is passed through a rubber sealed aperture in the plenum. The wiper
arm attachment to the splined shaft has a pivot to which the remainder of the arm is attached. The two parts of the
arm are connected by a spring which controls the pressure of the blade on the screen to a predetermined amount.
The wiper blades are attached to the wiper arms with a clips that allow the blade to pivot. Each wiper blade comprises
a number of levers and yokes to which the rubber wiper is attached. The levers and yokes ensure that the pressure
applied by the arm spring is distributed evenly along the full length of the blade. The rubber wiper is held in the yokes
by a pair of stainless steel strips which also contribute to the even distribution of spring pressure along the blade. The
driver's side wiper blade is fitted with an aerofoil which presses the blade onto the screen at high speed. This prevents
the blade from lifting off the screen and maintains the wiping performance.