System Overview
Heating and Ventilation UnitThe heating and ventilation and air conditioning unit is standard on all models, except Defender. The air conditioning system is an additional module, which provides fully integrated temperature control for the vehicle interior.
The 'Heating Ventilation Unit' controls the vehicles interior heating and air distribution, while the air conditioning module provides refrigerated air.
1. Fresh air inlet
2. Recirculation air inlet
3. Air outlets screen de-mist
4. Air outlet front/rear foot wells
6. Air outlet face level vents
7. Fresh/recirculation air door servo
8. Fresh/recirculation air door control valve
9. Water connections to heater core
10. Inlet manifold connection to reservoir and servo valve
Through-flow Ventilation
Flow-through ventilation is achieved by means of a one-way air extraction vent incorporated in the rear quarter "E" body panels. The vent opens and closes automatically depending on the heating and ventilation control settings and the volume of air entering the vehicle. Only one vent opening is actually used. After 1993 the left vent was blocked off to reduce ambient noise in the vehicle.
NOTE: For maximum A/C, switch "A" should be in the down position.
Heating and Ventilation Unit, Controls
The 'Heating and Ventilation Unit' is centrally located in the dash assembly. The air conditioning unit includes an evaporator with twin fans (from 1991) mounted to the right of the 'heating and ventilating unit'. A single fan was used until 1990.
The dash mounted central controls are used to operate both systems.
Heating and Ventilation Flaps and Controls
1. Fresh air vent (outside vehicle)
2. Recirculation vent (inside vehicle)
3. Air outlets screen de-mist
4. Air outlet front/rear foot wells
5. Air outlet for air conditioning
6. Air outlet face level vents
7. Heater radiator connections
A. Face level door and control
B. Air temperature coupled door and control
C. Screen de-mist wells coupled door and control
D. Fan speed control
E. Fresh and recirculation air door and control
NOTE: Control E also switches on the air conditioning system.
Heater Operation
The heating and ventilating unit consists of a heater core that is connected to the engine cooling system and a three speed fan for air circulation. As water is circulated through the heater core continuously, selection of hot or cold air is achieved by the operation of air doors that direct the air flow through the unit.
Control 'E' Operation Recirculated Air
This control when positioned to the right operates an electrical switch, vacuum valve and servo, which with the engine running, causes door E to close fresh air vent 1 and open recirculation air vent 2.
Fresh Air
Moving the control to the left switches off the vacuum and door E which is spring loaded, opens the fresh air vent A and closes the recirculation vent 2.
Control 'A' Operation - Face Level Vent
This control is mechanically connected to the face level door A and controls the volume of air exiting vent 6. Only fresh or re-circulated air is available from the face level vents 6.
Control 'B' Operation
This control mechanically operates two doors B which are coupled and divert the flow of air through the heater core to vary the temperature.
Control 'C' Operation
This control mechanically operates two coupled doors C which distribute air to the screen and footwells.
Control 'D' Operation
This is an electronic control for fan D and provides three speeds and an off position.
Air Conditioning
The air conditioning ON/OFF switch is operated by control 'E' and an electronic thermostat is connected to control B. (1987-1989 models used an electro/mechanical thermostat).
Controls 'E' must be moved fully to the left to switch on the air conditioning system and moving control 'B' to the left selects the degree of cooling required.