To cool the air within an A/C system, the refrigerant needs to reach optimum temperature and pressure. To help it reach this state, expansion valves inject the right amount of liquid refrigerant (mist) into the evaporator. This control over injection helps the evaporator lower the pressure and temperature of the refrigerant efficiently.
Expansion valves also help maintain conditions within the A/C system. They do this by adjusting the quantity of refrigerant injected according to the temperature of the superheated gas at the evaporator outlet. This ensures refrigerant can be converted from a liquid (mist) into a gas efficiently.