Which oil type is commonly used in modern refrigeration systems and is susceptible to hydrolysis in the presence of moisture?

• A. Mineral oil
• B. POE oil
• C. Ester oil
• D. Silicone oil

Answer: (B)

Polyol ester (POE) oil is commonly used in modern refrigeration systems with today’s refrigerants (like the HFCs). POE oil is hygroscopic, meaning it readily absorbs moisture from the air. When moisture is present, hydrolysis can occur, breaking the ester bonds and forming acids and alcohols. Those acids can corrode metals and cause sludge, degrading lubrication and potentially harming the compressor. That’s why POE’s moisture sensitivity is a key consideration in service—systems must be kept dry and properly dehydrated.

Mineral oil isn’t used with modern refrigerants due to poor compatibility and lubrication performance. Silicone oil isn’t standard for compressor lubrication in these systems. Ester oils exist in general, but POE is the usual choice for today’s refrigeration, precisely because of its performance with modern refrigerants and its moisture-related vulnerability.