The four major components of a vapor compression refrigeration system are the compressor, condenser, evaporator, and ______.

• A. Evaporator
• B. Metering Device
• C. Condenser
• D. Compressor

Answer: (B)

The key idea is that a vapor compression cycle needs a throttling element to control how much refrigerant can enter the evaporator. After the refrigerant is compressed and condensed, it must be expanded and pressured down before it can absorb heat in the evaporator. That job is done by the metering device, often a thermostatic expansion valve or a capillary tube. It throttles the high-pressure liquid, drops its pressure and temperature, and meters the flow to match the cooling demand. This control prevents flooding of the evaporator with liquid refrigerant and ensures the evaporator produces proper cooling by absorbing heat efficiently. The other three components—compressor, condenser, and evaporator—are already part of the cycle; the metering device is the missing fourth element that makes the system work smoothly.