This component usually stays at the evaporator inlet on the liquid line. In some cases the expansion valves are just off the condenser.
The expansion valve has similar function to the capillary tube, that is, both of them reduce the fluid pressure and decrease the temperature. However, the expansion valve has an additional function of controlling the amount of refrigerant flowing to the evaporator. Some expansion valves are fabricated with a small screen at the inlet, which serves as a filter to prevent metal particles from entering the valve. These small particles originate mainly from the compressor, since they are detached in the process of mechanical movements made by the compressor.
Note: In the case of valves that have small screens at the inlet, they may be clogged if there are too many particles. In this case it is important that these small screens are cleaned or if they look bad, they are replaced.
Description of operation
As the name itself suggests, the expansion valve causes the refrigerant to expand in it. In this way the fluid loses pressure. The expansion valve is between the high pressure environment that is on the condenser side and the compressor side and the low pressure side that goes from the evaporator until it reaches the compressor through the suction line.
The valve has a temperature sensor bulb
This bulb is attached to the refrigerant line at the evaporator outlet.
Note: Each expansion valve is designed for coolant fluid between -30ᵒC to - 12 acimaC above the evaporation temperature. Then the expansion valve bulb which is attached to the suction line at the outlet of the evaporator captures the temperature present therein and causes the valve to open and close as if it were a faucet according to the temperature present at the outlet of the evaporator.
In this way, when the temperature of the fluid over the set-point, the valve opens more and allows a greater flow of refrigerant fluid to flow towards the evaporator. So the flow cools more. However, when the temperature drops below the set point, the valve closes more allowing less refrigerant fluid to flow into the evaporator. In this way the temperature starts to rise either, the fluid becomes less cold. For which expansion valve to work properly two factors below should be observed:
1- It is important that the expansion valve is firmly attached to the tube at the outlet of the evaporator.
The valve must be set correctly according to the superheat calculation
