An expansion valve injects the high-temperature and high-pressure liquid refrigerant, which has passed through the receiver, from the small hole to cause the refrigerant to expand suddenly and to change it into the low-temperature and low-pressure mist refrigerant.
According to the cooling load, the expansion valve adjusts the refrigerant amount to supply to the evaporator.
The valve directly detects the refrigerant temperature (cooling load) around the outlet of the evaporator by the heat-sensing rod and transmits it to the gas inside the diaphragm. The change of the pressure of the gas due to the temperature change and the balance between the pressure of the outlet of the evaporator and that of the pressure spring moves the needle valve to adjust the amount of the refrigerant flow.
The temperature around the outlet of the evaporator changes according to the cooling load.
When the cooling load is small, the temperature around the outlet of the evaporator goes down, and the temperature transmitted from the heat-sensing rod to the gas inside the diaphragm also goes down, which makes the gas contract. As a result, the needle valve is pressed by the outlet refrigerant pressure of the evaporator and the pressure spring pressure, and moves to right. Closing the valve decreases the amount of the refrigerant flow and lowers the cooling capability.
When the cooling load is large, the temperature around the outlet of the evaporator increases and the gas expands. As a result, the needle valve moves to left, pushing the pressure spring. Opening the valve increases the amount of the refrigerant circulating in the cycle and makes the cooling capability higher.
The temperature sensing part of the expansion valve is attached to the outside of the outlet of the evaporator. At the top of the diaphragm that leads to the heat sensing tube, refrigerant gas is contained and the pressure of the gas changes depending on the temperature at the outlet of the evaporator.
The refrigerant pressure at the outlet of the evaporator is applied at the bottom of the diaphragm.
The balance between the force to press the diaphragm up (refrigerant pressure at the outlet of the evaporator + spring force) and the refrigerant pressure of the heat sensing tube moves the needle valve to adjust the refrigerant flow.
The function and operation of this type are same as that of the box type.
An evaporator evaporates the mist refrigerant, which is made low-temperature and low-pressure at the expansion valve, and cools the air around the evaporator.
This consists of a tank, tubes and cooling fins. The tubes penetrate through a number of cooling fins and form minute passages for good conductivity.
A blower motor fan forces air to the evaporator. The refrigerant removes the heat of evaporation from the air and is heated into a gas.
When the air that has passed the evaporator is cooled, the moisture in the air condenses and attaches to the cooling fin. The moisture becomes droplets and is stored in the drain pan to be drained out of the vehicle through the drain hose.