Liquid refrigerant entering the evaporator from the refrigerant flow control device is suddenly under which pressure?

• A. High
• B. Low
• C. Ambient
• D. Medium

Answer: (B)

The flow-control device creates a big pressure drop, so the liquid refrigerant entering the evaporator is at a low pressure. That throttling expansion lowers both the pressure and the temperature, bringing the refrigerant to the low evaporator pressure at which it can absorb heat and begin to boil inside the evaporator. In other words, after passing through the metering device, the refrigerant is left at a much lower pressure than in the condenser, which is what enables efficient heat absorption in the evaporator.