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

 The expansion device has the role of regulating the passage of the refrigerant flow in the evaporator and consequently the amount of steam to be sucked by the compressor. In addition, the expansion device ensures the pressure reduction of the fluid leaving the condenser and entering the evaporator, and a constant superheat is maintained through the sensor bulb at the outlet of the evaporator. This is achieved by letting more or less (automatically) coolant flow to the evaporator. Expansion valves can be externally equalized (the pressure at the top of the diaphragm is that of the evaporator outlet) and with internal equalization, ie the pressure at the bottom of the diaphragm is the inlet pressure of the evaporator.