Expansion Valve: Function
If the heat load of the air conditioner system increases, the refrigerant temperature at the evaporator outlet rises and therefore increases the pressure P1 at around the temperature sensing area. As this pressure P1 becomes higher than the resultant force of evaporator outlet (low pressure side) pressure P2 and the spring force F (P1 > P2 + F), the diaphragm is pressed down, opening the valve ball connected to the diaphragm to increase the flow of the refrigerant.
If the heat load decreases, the action contrary to the one mentioned above takes place, closing the valve to decrease the flow of the refrigerant.