Land Rover Discovery. Manual - part 189

AIR CONDITIONING

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.

AIR CONDITIONING

FAULT DIAGNOSIS

AIR CONDITIONING FAULTS

FAULT

CAUSE

REMEDY

1. Incorrect voltage.

1. Check voltage.

2. Open or defective fuse or relay.

2. Check and replace as necessary.

BLOWER

3. Loose wire connection including

3. Check system wires; tighten

MOTOR

ground.

all connections.

INOPERATIVE

4. Switch open or defective.

4. Replace switch.

OR SLOW

5. Tight, worn, or burnt motor

5. Replace motor.

RUNNING

bearings.

6. Open rotor windings.

6. Replace motor.

7. Worn motor brushes.

7. Replace motor.

8. Shaft binding-blade misaligned.

8. Check alignment. Repair or replace

as necessary.

9. Defective resistors

9. Rectify or replace.

1. Incorrect voltage.

1. Check voltage.

2. Open or defective fuse or relay.

2. Check and replace as necessary.

3. Defective thermostat control or

3. Replace thermostat or

COMPRESSOR

pressure switch.

CLUTCH

4. Shorted or open field coil.

4. Replace coil.

INOPERATIVE

5. Bearing seized (clutch will not

5. Replace clutch pulley assembly.

disengage).

6. Refrigeration circuit problem causing

heavy load and excessive drive
torque.

6. Check and rectify.

1. Incorrect alignment.

1. Check alignment; repair as

necessary.

2. Loose belt.

2. Adjust to proper tension.

3. Compressor not mounted securely.

3. Repair as necessary.

COMPRESSOR

4. Bearing in clutch-pulley

4. Remove clutch and replace

CLUTCH

assembly not pressed in.

clutch pulley assembly.

NOISY

5. Low voltage to clutch.

5. Check connections and voltage.

6. Clutch will not spin freely.

6. Refer to B5 above.

7. Oil on clutch face.

7. Check compressor seals for leaks.

8. Slipping clutch.

8. Refer to C5 above. Then check air

gap.

9. Overloaded or locked compressor.

9. Repair or replace compressor.

10. Icing.

10. Check for suction line frosting.

Replace expansion valve if
necessary.
Replace receiver/drier if necessary.

1. Motor and/or blades improperly

1. Check mountings, adjust as

CONDENSER

mounted.

necessary.

VIBRATION

2. Foreign matter build-up on

2. Clean blades with a suitable

blades.

non-inflammable cleaner.

3. Excessive wear of motor bearings.

3. Replace motor.

AIR CONDITIONING

FAULT DIAGNOSIS

REFRIGERATION SYSTEM FAULTS

For any refrigeration system to function properly all
components must be in good working order. The unit
cooling cycle and the relationship between air
discharge temperature and ambient temperature and
the pressures at the compressor can help to
determine proper operation of the system.
The length of any cooling cycle is determined by such
factors as ambient temperature and humidity,
thermostat setting, compressor speed and air leakage
into the cooled area, etc. With these factors constant,
any sudden increase in the length of the cooling cycle
would be indicative of abnormal operation of the air
conditioner.
The low and high side pressures at the compressor
will vary with changing ambient temperature, humidity,
in-car temperature and altitude.
The following items should be checked before
operating the system:

1. Compressor drive belt tension.
2. Compressor magnetic clutch operation.
3. Condenser fan operation.
4. Condenser fins, dirt will cause poor cooling and

higher operating temperatures.

The following conditions should be checked after
operating the system for several minutes:

1. All high pressure lines and components should

be hot to the touch.

2. All low pressure lines should be cool to the

touch.

3. Inlet and outlet temperatures at the receiver/drier

should be at the same temperature (warm). Any
very noticeable temperature difference indicates
a blocked receiver/drier.

4. Heavy frost on the inlet to the expansion valve

may indicate a defective valve or moisture in the
system.

5. Evaporation air temperature will vary with

ambient temperature and humidity. As humidity
increases the outlet temperature will be higher.

AIR CONDITIONING

FAULT DIAGNOSIS

FAULT

CAUSE

REMEDY

1. Overcharge of refrigerant.

1. Discharge, evacuate and charge

system.

A.
HIGH HEAD

2. Air in system.

2. Discharge system, fit new drier,

PRESSURE

evacuate and charge system.

3. Condenser air passage clogged

3. Clean condenser of debris.

with dirt or other foreign matter.

4. Condenser fan motor defective.

4. Replace motor.

5. Incorrect voltage to fan motor.

5. Check voltage.

1. Undercharge of refrigerant;

1. Evacuate and charge system.

evident by bubbles in sight

Check for leakage.

LOW HEAD

glass while system is operating

PRESSURE

2. Split compressor gasket or

2. Replace gasket and/or reed

leaking valves.

valve. Fit new drier, evacuate and
charge system.

3. Defective compressor.

3. Repair or replace compressor.

1. Loose drive belt

1. Check belt tension.

2. Refrigerant flooding through

evaporator into suction line; evident
by ice on suction line and suction
service valve.

2. Check thermobulb. Bulb should be

securely clamped to clean horizontal
section of copper suction pipe.

3. Expansion valve stuck open.

3. Replace expansion valve.

HIGH

4. Leaking compressor valves,

4. Replace valves and/or

SUCTION

valve gaskets and/or service

gaskets. Fit new drier

PRESSURE

valves.

evacuate and charge system.

5. Receiver/drier blocked; evident

5. Fit new drier, evacuate

by temperature difference

and charge system.

between input and output lines.

1. Expansion valve thermobulb not

1. Warm thermobulb with hand.

operating.

Suction should rise rapidly to 1.4 bar
20 lb/in

or more. If not replace

expansion valve.

2. Expansion valve sticking closed.

2. Check inlet side screen.

Clean if clogged. Refer

LOW

to C-2 and C-3.

SUCTION

3. Moisture freezing in expansion valve

orifice. Valve outlet tube will frost
while inlet hose tube will have little or
no frost. System operates
periodically.

3. Fit new drier, evacuate and charge

system.

4. Dust, paper scraps, or other debris

restricting evaporator blower grille

4. Clean grilles as required.

5. Defective evaporator blower motor,

wiring, or blower switch.

5. Refer to Fault Diagnosis Chart for

blower motor.

Content .. 187 188 189 190 ..