In an air conditioning system that uses a TXV, the evaporator outlet temperature is usually

• A. Warmer than the evaporator inlet
• B. Colder than the evaporator inlet
• C. Equal to the evaporator inlet
• D. Variable and unpredictable

Answer: (A)

When refrigerant enters the evaporator, it’s at a low pressure and is either a cold liquid or a cold liquid–vapor mixture. As it moves through the evaporator, it absorbs heat from the surrounding air. That heat addition raises the refrigerant’s temperature as it boils and then exits as low-pressure vapor, often with some superheat. Because energy is being added in the evaporator, the temperature rises from inlet to outlet. So the outlet is warmer than the inlet.

This isn’t about the refrigerant leaving cooler or at the same temperature—the system is designed to absorb heat, not remove it in that direction. While there is some variation with load, the general behavior with a TXV is a warmer outlet due to the heat transfer and phase change occurring inside the evaporator.