What is the role of the expansion device in an air conditioning system?

The expansion device has a role in regulating the passage of refrigerant flow to the evaporator and hence the amount of steam to be sucked by the compressor. Furthermore, the expansion device ensures a reduction in fluid pressure exiting the condenser and enters the evaporator and also through a sensing bulb is maintained constant superheat at the evaporator outlet. This is accomplished by leaving more or less pass (automatically) refrigerant to the evaporator. The expansion valves can be with external equalization (pressure at the top of the diaphragm is the evaporator outlet) and internal equalization, i.e., the pressure at the bottom of the diaphragm is the evaporator inlet pressure.