Air conditioners have many parts that are very important in their continuous function, from the compressor to the refrigerant coils. The expansion valve has the function of limiting the flow of refrigerant through the system.
Meaning
Without an expansion valve, your air conditioner would simply blow air with no effect on temperature, due to the uncontrolled flow rate of the internal refrigerant gas. With a little pressure, your refrigerant cools down as it passes through the evaporator coils and gives you the cool breeze of cool air that you anticipate when turning on the air conditioning unit.
How the expansion valve works
The expansion valve regulates the flow of your refrigerant by compressing or expanding according to the amount of pressure your air conditioner needs to effectively vaporize the refrigerant inside. As it contracts, less refrigerant flows into the evaporator coils. The hot side of the refrigerant coils creates a pressure that causes the refrigerant inside the coil to have a tendency to move faster. The refrigerant that spends more time in the evaporator coils is cooled to a lower temperature as the heat is transferred to the water inside the coils.
What the valve controls
A bulb is located outside the expansion valve, which reacts at room temperature due to the refrigerant gas inside. This bulb has its own amount of gas dedicated to one side of the refrigerant that flows through the air conditioner and causes the bulb to go down as its temperature rises. When the gas bulb moves downward, the expansion valve rises, releasing some of the pressure on the gases within the coils leading to it.
Alternatives
Some air conditioning manufacturers choose to produce air conditioners with other types of flow control devices, such as capillary tubes and pistons, all of which serve the same purpose. Piston systems work with a simple mechanism that lowers the piston to regulate the flow of coolant. A capillary tube regulates the flow simply by getting thinner, with few moving parts involved in the process, if any. Even air conditioners with expansion valves use capillary tubes that connect to the valve.