What is superheat and why is it important?

• A. The temperature rise of vapor above its saturated temperature; ensures only vapor enters the compressor and protects the compressor.
• B. The temperature rise of liquid above its boiling point.
• C. The ambient air temperature.
• D. The refrigerant pressure.

Answer: (A)

Superheat is the temperature rise of the refrigerant vapor above the saturated temperature at the evaporator pressure. In practice, you measure the vapor’s temperature as it leaves the evaporator (in the suction line) and compare it to the temperature at which the refrigerant would start to boil at the same pressure. The difference is the superheat.

This concept matters because it ensures only vapor enters the compressor, protecting it from liquid slugging and potential damage. It also indicates how much heat the evaporator has absorbed: enough superheat means the evaporator is doing its job, while too little suggests liquid refrigerant could be returning to the compressor, and too much means the evaporator isn’t being utilized efficiently. In many systems, superheat is used to help manage refrigerant charge and operating stability.

The other ideas described—liquid overheating, ambient air temperature, or refrigerant pressure—do not define superheat.