System Operation

The air conditioning system provides the means of supplying cooled and dehumidified, recirculated air to the interior of the vehicle. The cooling effect is obtained by blowing air through the matrix of an evaporator unit which has a variable temperature control to provide the conditions required inside the vehicle. The volume of cooled air supplied is controlled by a variable speed blower.

A sealed system, charged with Refrigerant R134a, together with a blower unit and evaporator temperature control combine to achieve the cooled air condition.

The air conditioning system comprises six major units:
1. An engine-mounted compressor.
2. A condenser mounted in front of the radiator.
3. A receiver/drier unit mounted on RH front valance.
4. Thermostatic expansion valve mounted in front of the evaporator.
5. An evaporator and blower unit mounted under the RH side of the fascia panel.
6. Blower and temperature control switches.

These units are interconnected by hoses and pipes carrying Refrigerant R134a, the evaporator is separate from the vehicle ventilation system.

Refrigeration cycle

1. Compressor
The compressor (1), belt driven from the crankshaft pulley, is brought into operation by an AC switch on the fascia which when selected engages an electron-magnetic clutch to operate the compressor, which pressurizes and circulates the refrigerant through the system. The 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 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 trinary 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 condenser cooling fan operates continuously when air conditioning is selected.

2. Condenser
From the compressor, hot high pressure vaporized 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 the cooling fan (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, 23 °F it boils and vaporizes.

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 blower fans which can be operated at various 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 atomized 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 positioned in the airflow leaving 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.