What is the purpose of the metering device in a vapor compression system?

• A. Meters the flow of refrigerant entering the evaporator, increasing the boiling point to create a pressure/temperature drop
• B. Meters the flow of refrigerant entering the evaporator, reducing the boiling point to create a pressure/temperature drop
• C. Removes air from the system
• D. Keeps refrigerant always at high pressure

Answer: (B)

The metering device throttles refrigerant into the evaporator, creating a controlled pressure drop. That reduction in pressure lowers the refrigerant’s boiling point, so as it enters the evaporator it can absorb heat from the space and begin to vaporize. This evaporation is what removes heat and produces the cooling effect. The device also helps regulate how much liquid refrigerant enters the evaporator to prevent floodback and maintain proper system balance. It does not remove air from the system, it does not keep refrigerant at high pressure, and it does not raise the boiling point; it lowers the pressure to allow evaporation to occur.