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.

EXPANSION  DEVICE:    
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 Device's 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. 

EVAPORATOR:               
As soon as the liquid pressure drops, the refrigerant begins to boil (R134A refrigerant boils at approximately -26 degrees centigrade).  As it continues to boil the Evaporator absorbs the heat passing over its tubes and fins and as a result the air is cooled.  Remember that heat is being removed from the warm air and cold air is not being created.  The compressor, on its suction side, removes the low pressure vapour from the Evaporator and the cycle starts all over again.