How It Works
The Compressor transports the refrigerant at the required pressure through the air conditioning system. The refrigerant is a low-pressure gas as it enters the Compressor from the Evaporator. The Compressor increases the refrigerant pressure and its temperature so it becomes a high-pressure gas which, in turn, helps the refrigerant condense more rapidly in the next component, which is the Condenser. The Compressor is mounted on the engine and is driven by a belt from the engine's crankshaft pulley. The most common reasons for failure are lack of oil, pulley bearing wear, electromagnetic coil burn-out and lack of regular servicing.
The Condenser works in the opposite way to the Evaporator. The refrigerant gives up its heat generated by the Compressor by passing cold air across its fins and tubes by ram air or by an extra fan. The end result of this change is that the refrigerant is now a high-pressure liquid and is forced out to the Receiver Drier through the liquid line. Because the Condenser is usually located at the front of the vehicle it can become damaged by debris or corroded by materials from the road. It can also fail because of weak spots in its construction and lack of regular servicing.
Depending on the type of air conditioning system fitted, this item can be called a Receiver Drier or an Accumulator. (The Accumulator is fitted on the low-pressure gas line of an air conditioning system between the Compressor and the Evaporator and is used in conjunction with an orifice tube). The Receiver Drier is fitted on the high-pressure liquid line of an air conditioning system between the Condenser and Expansion Device.
The Receiver Drier has two parts to it, the receiver and, of course, the drier. The receiver section holds the right amount of refrigerant required by the system to ensure correct operation and to supply a steady flow of liquid refrigerant to the Expansion Device. The drier section is responsible for removing moisture from the air conditioning system by means of a bag of desiccant which absorbs small quantities of moisture. This is a very important part of the air conditioning system and should be changed at least every two years or when the system is repaired. The most common reasons for failure is corrosion and desiccant deterioration which leads to severe system failure.
The Expansion Device comes in many forms. It can be a brass internally or externally equalised valve, a block type valve or an orifice tube (the latter being part of an Accumulator type air conditioning system). Expansion Devices have an inlet and an outlet which separates the high side of the system from the low side. A small restriction in the valve allows only a small amount of refrigerant to pass through it into the Evaporator, the amount of refrigerant passing through the valve depends on the Evaporator temperature. The most common reasons for failure are contamination, moisture and lack of regular servicing.
Air Conditioning – the Science Behind it
Firstly, wet your finger and wave it in the air. What you are feeling is a refrigeration effect. When liquid turns to a vapor it absorbs heat. In this case it is sucking the heat out of your finger. The opposite is also true. If that vapor then loses that heat, it turns back into a liquid. In a refrigeration system, we force a liquid to become a vapor in the evaporator, thus absorbing heat from the refrigerated space. We then use a compressor to pump that vapor to the condenser. In the condenser, we force that vapor to reject the heat and thus turn back into a liquid so that we can re-use it. We then meter the liquid back into the evaporator to complete the loop and do it all over again and again and again.
How Do We Force a Liquid to Become a Vapor?... Or a Vapor To Become a Liquid?
The boiling point needs to be manipulated to change into a vapor or for the vapour to become a liquid. The boiling point is the temperature at which the liquid turns to vapor when heat is added. It is also the temperature at which a vapor turns to liquid when heat is removed.
Boiling point = saturation temp = evaporating temp = condensing temp
In the evaporator, we force liquid to become a vapor by lowering its pressure until its boiling point/evaporating temperature is lower than the air it is trying to cool. In the condenser, we force the vapor to become a liquid by raising its pressure until its boiling point/condensing temperature is higher than the air it is trying to heat. Different substances have different boiling points at different pressures. We can tell what the boiling point/saturation temp/evaporating temp/condensing temp is at various pressures for common refrigerants by checking a pressure/temperature chart.