Which oils are commonly used in refrigerant systems, and what steps help prevent cross-contamination when replacing oil?

• A. Mineral oil, POE, and PAG; flush the system, avoid mixing incompatible oils, and label the oil type used.
• B. Vegetable oil and silicone oil; mix freely and reuse old oil.
• C. Only mineral oil; assume compatibility with all refrigerants.
• D. Synthetic oil only; ignore compatibility.

Answer: (A)

Different refrigerants require different lubricants, and not all oils mix well together. Mineral oil is typical in older systems, while modern systems often use POE or PAG oils. Mixing these incompatible oils can cause lubrication problems, oil migration, and compressor damage, so it’s essential to prevent cross-contamination.

To avoid cross-contamination when replacing oil, flush the system to remove residual oil, replace filters or the drier, and use the correct oil type for the refrigerant in use. labeling the oil type used helps ensure future servicing uses the right lubricant, preventing accidental mixing.