NATE Air Conditioning and Heat Pumps Practice Exam

What effect does raising the pressure in a sealed system have on refrigerant?

1. It becomes more difficult to subcool the liquid refrigerant

2. It becomes more difficult to superheat the refrigerant vapor

3. The refrigerant's boiling point decreases

4. The refrigerant's boiling point increases

The correct answer is: The refrigerant's boiling point increases

Raising the pressure in a sealed refrigeration system causes the boiling point of the refrigerant to increase. This is due to the relationship established by the pressure-temperature characteristics of refrigerants found in their respective phase diagrams. When the pressure is increased, more energy is required for the refrigerant to transition from a liquid to a vapor state, thereby raising its boiling point. In practical terms, this means that under higher pressure conditions, the refrigerant will remain in liquid form over a broader range of temperatures before it eventually boils. This principle is essential in understanding how refrigerants operate within various HVAC applications, ensuring efficient heat exchange and system performance.