An ideal oil is readily miscible with the refrigerant in the system.

• A. Sometimes
• B. Not specified
• C. True
• D. False

Answer: (C)

Oil compatibility with the refrigerant is crucial for proper lubrication and oil return in a vapor-compression system. If the oil is readily miscible with the refrigerant, it rides along with the refrigerant as it circulates, ensuring the compressor stays lubricated and oil can be carried back to the compressor via the refrigerant flow. In the ideal scenario, this miscibility is assumed to be complete, so the statement “an ideal oil is readily miscible with the refrigerant in the system” is true. In real systems, oils are selected to be compatible with the refrigerant to promote this same behavior; when miscibility is poor, oil can separate and cause lubrication problems.