In an air conditioning system that uses a thermostatic expansion valve, the temperature of the evaporator outlet will usually be...

• A. Warmer than the evaporator inlet
• B. Colder than the evaporator inlet
• C. Equal to the evaporator inlet
• D. Much warmer than the evaporator inlet

Answer: (A)

In the evaporator, the refrigerant enters cold and at low pressure after the expansion valve, then absorbs heat from the air flowing across the coil. As it takes in this energy, the refrigerant boils and changes from liquid toward vapor, so its temperature rises along the path through the evaporator. The result is that the refrigerant leaving the evaporator is warmer than what entered, with its temperature tied to the evaporator’s pressure (the saturation temperature at that low pressure). So, the evaporator outlet is warmer than the evaporator inlet.