Which two refrigerant oils cannot be mixed?

Which two refrigerant oils cannot be mixed?

• A. PAG oil and mineral oil
• B. Mineral oil and ester oil
• C. PAG oil and POE oil
• D. Ester oil and mineral oil

Answer: (A)

Oil compatibility in refrigeration systems is crucial because different oil types don’t always blend together. Polyalkylene glycol (PAG) oil is polar, while mineral oil is nonpolar. These fundamental differences make PAG and mineral oil immiscible, so if they are mixed they separate into distinct layers rather than forming a uniform oil blend. That separation means oil won’t circulate properly, lubrication becomes inconsistent, and bearing wear or compressor damage can occur. Sludge and poor oil film formation can also result, further endangering the compressor. When servicing, if PAG ends up mixed with mineral oil, the system should be flushed and the oil replaced to restore proper lubrication. The other pairings do not pose the same immediate, universal incompatibility as PAG with mineral oil, which is why this combination is the best answer.

Oil compatibility in refrigeration systems is crucial because different oil types don’t always blend together. Polyalkylene glycol (PAG) oil is polar, while mineral oil is nonpolar. These fundamental differences make PAG and mineral oil immiscible, so if they are mixed they separate into distinct layers rather than forming a uniform oil blend. That separation means oil won’t circulate properly, lubrication becomes inconsistent, and bearing wear or compressor damage can occur. Sludge and poor oil film formation can also result, further endangering the compressor. When servicing, if PAG ends up mixed with mineral oil, the system should be flushed and the oil replaced to restore proper lubrication.

The other pairings do not pose the same immediate, universal incompatibility as PAG with mineral oil, which is why this combination is the best answer.