1995 LAND ROVER DISCOVERY coolant temperature

80HEATING AND VENTILATION
4
DESCRIPTION AND OPERATION Air direction flap
Flap moves across mixing chamber to direct the air
flow away from the heater matrix.
Air temperature flap
Control at HOT, flaps fully closed. All air flow passes
through heater matrix. As control is moved towards
COLD the flaps progressively open directing air flow
away from the heater matrix.
Control at COLD, flaps fully open.
V8 Engine:When both controls are at COLD, 2
micro-switches are closed and operate a vacuum
valve which closes the coolant valve.Air conditioning
When an air conditioning unit is fitted, the mechanical
operation of the heater controls remains unaltered.
However the air conditioning evaporator is positioned
in front of the mixing chamber through which all air
flow passes.

HEATING AND VENTILATION
1
FAULT DIAGNOSIS HEATER OUTPUT
Symptom:-
Heater emits cold air.
1.Engine running: Check coolant valve opens as a
temperature control is moved from COLD.
2.Check for engine running cold.
See COOLING
SYSTEM, Fault diagnosis, Engine Runs Cold
3.Check heater pipes and hoses for blockage or
restriction.
4.Check heater matrix for blockage or restriction,
flush system.
Heater emits warm air.
5. Engine running:Check coolant valve closes
when both temperature controls are moved to
COLD.

AIR CONDITIONING
3
DESCRIPTION AND OPERATION AIR CONDITIONING SYSTEM OPERATION
The air conditioning system provides the means of
supplying cooled and dehumidified, fresh or
recirculated air to the interior of the vehicle. The
cooling effect is obtained by blowing air through the
matrix of an evaporator unit and when required,
mixing that air with heated air by means of the heater
distribution and blend unit, to provide the conditions
required inside the vehicle. The volume of conditioned
air being supplied is controlled by a variable speed
blower.
A sealed system, charged with Refrigerant R134a,
together with a blower unit, blend unit and control
system combine to achieve the cooled air condition.
For air conditioning air distribution system.
See
HEATING AND VENTILATION, Description and
operation, Heating and ventilation unit
The air conditioning system comprises five major
units:
1.An engine-mounted compressor.
2.A condenser mounted in front of the radiator.
3.A receiver/drier unit located in front of the
condenser.
4.Thermostatic expansion valve mounted above
the evaporator.
5.An evaporator unit mounted in front of the heater
matrix.
NOTE: Vehicles fitted with rear air
conditioning have an additional
evaporator/blower motor assembly located
behind the LH rear compartment lower trim panel.
These units are interconnected by hoses and pipes
carrying Refrigerant R134a, the evaporator is linked
into the vehicle ventilation system.
Refrigeration cycle
1. Compressor
The compressor (1), belt driven from the crankshaft
pulley, pressurises and circulates the refrigerant
through the system. Mounted on the compressor, an
electro-mechanical clutch maintains the correct
temperature and pressure by engaging or disengaging
to support the system's requirements. The clutch
action is normally controlled by a thermostat located
at the evaporator (5). The compressor is of the
swashplate type having fixed displacement.Should the temperature at the evaporator (5) fall low
enough for ice to begin to form on the fins, the
thermostat disengages the clutch and also isolates the
cooling fans relays. When the temperature at the
evaporator (5) rises to the control temperature, the
clutch is re-engaged.
Should the system pressure become excessive or
drop sufficiently to cause damage to the compressor
(1) a dual pressure switch (7), located in the high
pressure line, signals the relay unit to disengage the
clutch. The compressor also has an emergency high
pressure relief valve (9) fitted.
The cooling fans are controlled by engine temperature
when the air conditioning is not switched on.
2. Condenser
From the compressor, hot high pressure vaporised
refrigerant (F1) passes to the condenser (2), which is
mounted in front of the engine coolant radiator. Ram
air(A1) passing through the condenser (2),
supplemented by 2 cooling fans (8) mounted in front
of the condenser, cools the refrigerant vapour
sufficiently to form a high pressure slightly subcooled
liquid (F2).
3. Receiver/drier
This liquid then passes to a receiver/drier (3) which
fulfils two functions. It acts as a reservoir and moisture
extractor (11).
A sight glass (10), in the high pressure line, provides a
method of determining the state of the refrigerant
without breaking into the system.
4. Expansion valve
From the receiver/drier (3) the moisture free high
pressure liquid refrigerant (F3) passes through a
thermostatic expansion valve (4). A severe pressure
drop occurs across the valve and as the refrigerant
enters the evaporator space at a temperature of
approximately -5°C it boils and vaporises.

82AIR CONDITIONING
4
DESCRIPTION AND OPERATION 5. Evaporator
As this change of state occurs, a large amount of
latent heat is absorbed. The evaporator is therefore
cooled and as a result heat is extracted from the air
flowing across the evaporator. The air flow is
controlled by the ventilation fan which can be
operated at anyone of four speeds.
To prevent liquid passing through to the compressor,
a capillary tube (6), attached to the outlet pipe of the
evaporator (5) and connected to the thermostatic
expansion valve (4), controls the amount that the
valve opens and closes in relation to the temperature
of the low pressure high temperature refrigerant
vapour (F4) at the outlet. The atomised refrigerant
then passes through the evaporator (5). Fan blown air
(A2) passes through the matrix (A3) of the evaporator
and is cooled by absorption due to the low
temperature refrigerant passing through the
evaporator.
A thermostat is fitted in the airflow out of the
evaporator to sense the temperature of the exterior
fins. Should ice begin to form, due to a too cold
condition, it will signal to disengage the
electro-mechanical clutch on the compressor (1).
From the evaporator, low pressure slightly
superheated refrigerant (F5) passes to the
compressor to complete the cycle.AIR CONDITIONING CONTROL SYSTEM
The air conditioning control system comprises relays,
thermostat, pressure switches, and a control panel.
Inputs from outside the air conditioning system
comprise temperature information from the engine
cooling system. Together these controls, in
conjunction with the cooling fans, compressor clutch,
blower and heater distribution and blend unit enable
minimal input to maintain the required environment
inside the vehicle.
When air conditioning is not selected, air is supplied
by ram effect or blower to the areas selected by the
controls. The air mix flap on the blend unit controls the
temperature of the air being supplied. No cooled air is
available.
Selecting air conditioning provides the added facility of
cooled air available to be mixed as before. When
required a fully cold condition can be selected by
turning the temperature controls to cold, which
automatically closes the heated coolant access to the
heater matrix. Mixtures of cooled, fresh, and hot air
can be selected to give required interior environmental
conditions by selection at the control panel.
Dual pressure switch
This switch, located in the high pressure line between
the receiver drier and the expansion valve, monitors
refrigerant pressure and by means of the relay module
controls the following system functions:
1.Refrigerant pressure drops below 2.0 bar, 29
lbf/in
2(due to possible leakage), the
compressor's electro-mechanical clutch is
dis-engaged.
When pressure rises above 2.0 bar, 29 lbf/in
2the
compressor's clutch is re-engaged.
2.Refrigerant pressure rises above 32 bar, 455
lbf/in
2(due to possible blockage), even with
cooling fan operation, the compressor's
electro-mechanical clutch is dis-engaged.
When the pressure drops below 26 bar, 375
lbf/in
2the compressor clutch is re-engaged.

AIR CONDITIONING
5
DESCRIPTION AND OPERATION Condenser cooling fans
The condenser cooling fans operate automatically
whenever the air conditioning system is switched on.
Fan timer unit
The thermostatically controlled timer will continue to
operate the cooling fans after the air conditioning or
ignition is switched off. When the system temperature
is excessive, the fans will operate for 10 minutes to
reduce condenser and underbonnet temperature.
Blower control
The blower can be operated at any one of four speeds
by sliding the blower switch to the required position.
When the blower is switched off the air conditioning
system will not operate.
The fresh air/recirculation flaps can move between
two positions. One position covers the outside air
inlet, leaving open an inlet from the inside of the
vehicle clear, when recirculated air is required. In the
other position they will cover the inlet from the inside
of the vehicle leaving open the outside air inlet when
fresh air is required.Heater distribution and blend unit control
Blower unit air flow, having passed through the
evaporator passes into the heater blend unit to be
heated, if required. It is then directed into the vehicle
interior in accordance with the flap positions
designated by the air distribution control. Heater flaps
control the amount of air flowing through the heater
matrix. These flaps are controlled individually by the
driver's and passenger's temperature controls.
When the temperature control is in the cold position, a
micro switch actuates a vacuum control to close the
coolant valve on the engine. As the temperature
control is moved away from cold, the coolant valve is
opened allowing heated engine coolant to flow
throught the heater matrix. The temperature of the
heated air flow into the vehicle interior is controlled by
the blend flaps.
The distribution control moves the flaps which control
the direction of the air flow into the interior of the
vehicle.

ELECTRICAL
37
REPAIR COOLANT TEMPERATURE AND FUEL GAUGES
Service repair no - 88.25.14 - Coolant temperature
gauge
Service repair no - 88.25.26 - Fuel gauge
Remove
1.Remove instrument cowl.
See Instrument
cowl and illumination board
2.Remove speedometer trip reset button sleeve.
3.Remove instrument face plate.
Coolant temperature gauge
4.Remove circuit board,See Circuit board
5.Remove 3 screws securing coolant temperature
gauge to binnacle, remove gauge.
Fuel gauge
6.Remove 3 screws securing fuel gauge to
binnacle, remove gauge.
Refit
7.Reverse removal procedure.SPEEDOMETER TRANSDUCER
Service repair no - 88.30.14
Remove
1.Position vehicle on ramp and chock wheels.
2.Raise ramp.
3.Disconnect multiplug from transducer.
4.Remove bolt securing transducer, remove
transducer.
Refit
5.Reverse removal procedure.

ELECTRICAL
41
REPAIR COOLANT TEMPERATURE TRANSMITTER - V8i
Service repair no - 26.10.02
Remove
1.Disconnect battery negative lead.
2.Disconnect lead from transmitter.
3.Remove transmitter, discard sealing washer if
fitted.
Refit
4.Coat threads of replacement transmitter with
Loctite 572.
5.Fit a new sealing washer to transmitter.
6.Fit transmitter, connect lead.
7.Top-up cooling system.HEATED FRONT SCREEN
Heated front screen will operate when switch is
operated, with engine running. Timer unit will provide
a preset time cycle of 7« minutes±20%.
To identify timer unit.
See Electrical Trouble
Shooting Manual.Electrical Troubleshooting
Manual
Switching OFF ignition, or further operation of heated
front screen switch during cycle will switch off screen
and cancel, reset and switch off timer unit.