Function

Air conditioning

General




The air conditioning only functions at ambient temperatures above 0 °C. At temperatures lower than this, the pressure in the system is too low and the compressor is never engaged.
The air conditioning only functions when the engine is running. It functions regardless of engine speed (RPM) and vehicle speed. The blower fan must also be operating before the climate control system can be engaged.
The air conditioning system has only two positions, off and on. If it is too cold in the passenger compartment, the temperature can be controlled with the normal heat and blower fan controls.
Air conditioning is based on the same principle as that used in refrigerators.

Refrigerant




1. Compressor
2. Condenser
3. Engine cooling fan (FC)
4. Fixed throttle valve
5. Evaporator
6. Blower fan
7. Receiver.
Explanation:
A - High pressure, warm fluid
B - Low pressure, cold fluid
C - Low pressure, cold gas
D - High pressure, warm gas
Dark arrow - Warm air
Light arrow - Cold air
By allowing the refrigerant to circulate in the closed system and changing the pressure and volume it will change temperature and boil (evaporate). At the pressure found in the system, approximately 170 - 320 kPa (1.7 - 3.2 bar), the refrigerant boils at approximately 0 to +4 °C.
A condition of the refrigerant boiling is that the heat is accessible. This heat is taken from the air around the evaporator where boiling occurs. When the heat is taken up by the refrigerant the surrounding air becomes cooler. It is this cooled air that is blown into the passenger compartment by the climate control system blower fan. The heat taken up by the refrigerant in the evaporator is transported out to the engine compartment, where it is transferred to the air by the condenser. The condenser is cooled by the airflow and the engine cooling fan (FC).

Compressor




The task of the compressor is to:
- draw gaseous refrigerant from the evaporator
- compress the gas thereby increasing its pressure and temperature
- expel the gas with high pressure and high temperature to the condenser.
The compressor takes in cold refrigerant gas from the receiver on the intake side through the low pressure connection.
In ideal conditions, the compressor compresses the refrigerant from approximately 200 kPa (2 bar) to between 1.2 MPa and 2.1 MPa (12 and 21 bar). During the process, the refrigerant heats up from 0 °C to between 70 °C and 110 °C. These pressure and temperature values apply when the system is operating under optimal conditions.
The relief valve, located on the rear section of the compressor, functions as an extra safety device. The valve opens and releases refrigerant when the pressure in the system is too high (at approx. 3.5 MPa (35 bar)). The valve then shuts again when the pressure has returned to normal.
The temperature of the refrigerant gas can increase to as much as 125 °C.
The compressor can only compress gases, as liquid would damage the compressor.

Fixed throttle valve (orifice)




1. Inlet on the high pressure side
2. Filter insert
3. Internal diameter of the throttle valve
4. O-ring
5. Outlet on the low pressure side.
The task of the throttle valve is to:
- regulate the quality of refrigerant that flows through en route to the evaporator
- separate the high pressure side from the low pressure side.
Upstream of the throttle valve is the refrigerant in liquid form at high pressure.
The throttle valve ensures that the correct amount of refrigerant is released to the evaporator. The quantity of refrigerant must be sufficient that the final remains evaporate precisely before the evaporator outlet.
Too little refrigerant causes the refrigerant to evaporate quickly and the vapor to overheat. This results in reduced cooling capacity.
Too much refrigerant means that some of the refrigerant does not evaporate, but is heated up. This results in reduced cooling capacity. In addition there is the risk that some of the refrigerant in liquid form reaches the compressor. This may damage the compressor because liquid cannot be compressed.

Evaporator




The task of the evaporator is to cool and dry the air.
Heat is extracted from the air that flows over the outside of the evaporator housing. In this way, cooled air is directed into the passenger compartment. In the evaporator the heat is transferred from the warm air to the cold refrigerant. The refrigerant then begins to boil and evaporates.
The refrigerant, in liquid form, is injected into the evaporate in precisely measured volumes. The refrigerant evaporates as a result of the sudden drop in pressure and emits heat energy during this process.
When the air entering the passenger compartment encounters the cold evaporator, the humidity in the air condenses on the evaporator. The water drains out under the vehicle via a drain hose. In the event of high humidity, this may be considerable quantities of water, which is often mistaken for a water leak from the engine for example. Water that condenses binds and takes with it some of the dust and the larger impurities in the air. Therefore the air conditioning system also helps to purify the air.
The refrigerant volume that is measured by the throttle valve is injected into the evaporator. As soon as the refrigerant enters the cooling pipes, it evaporates due to the drop in pressure. During this process, heat is also extracted from the cooling pipes. The cooling pipes and the entire evaporator cool immediately. The refrigerant gas is then drawn out using the compressor.
The airflow through the evaporator is cooled and dried, and then forwarded to the passenger compartment via the air distribution ducts.
During this process, the moisture in the air condenses on the evaporator flanges. Dust, pollen, etc., which is deposited on the damp evaporator is rinsed away. This cleans and dries the air.

Receiver.




The task of the receiver is to:
- function as a filter, taking up and binding moisture (water) found in the system
- protect the compressor from refrigerant in the liquid phase (separates refrigerant in gaseous form and liquid form)
- function as a storage container for:
- refrigerant
- oil
- leak detection dye.
The leak detection dye mixes with the oil. When a leak occurs, it is possible to locate the leak with UV light.

Condenser (air cooled heat exchanger)




The task of the condenser is to cool, so converting the hot, gaseous refrigerant to a liquid.
The compressor pumps in hot refrigerant gas under high pressure. The gas has a temperature of between 70 and 110 °C in the intake on top of the condenser.
When the hot gas flows through the pipe loop, it is cooled down and condensed. The heat that is removed from the gas during this process is transferred to the surrounding air. The engine cooling fan (FC) increases the airflow through the condenser. This increases the transfer of heat from the refrigerant to the outside air.
The fan is controlled with the aid of a high pressure pressure switch or a linear high pressure sensor located in the refrigerant line. The fan is also controlled by the fan thermostat located in the coolant circuit.

Service valves




1. Service valve for emptying and vacuum pumping.
2. Service valve for emptying, vacuum pumping and filling of refrigerant.
The service valves are used for:
- checking the system through manometer connections
- draining the system of refrigerant
- vacuum pumping
- filling of refrigerant, which normally takes place on the low pressure side but can also take place on the high pressure side in an orifice system such as this.