What type of oil is recommended for use with refrigerant R404A?

Polyolester oil is the recommended type of lubricant for use with refrigerant R404A due to its chemical compatibility and performance characteristics. R404A is a blend of hydrofluorocarbon (HFC) refrigerants, and it requires a lubricant that can maintain stability under the operating conditions typical for these types of systems.

Polyolester oils have several advantages when used with HFC refrigerants. They provide good lubrication properties, have a high thermal stability, and are hygroscopic, which means they can absorb moisture, aiding in the prevention of corrosion in the system. Moreover, their compatibility with mineral oils is limited, which is a critical aspect to consider, since HFC refrigerants can degrade mineral oils, leading to inefficient system operation and potential damage over time.

In contrast, while PAG oil is suitable for some synthetic refrigerants, it is not specifically recommended for R404A. Mineral oil is incompatible with many of the modern refrigerants and could lead to performance issues. Castor oil is generally not used in refrigeration systems as it has undesirable characteristics for such applications. Thus, polyolester oil stands out as the most effective and suitable choice for ensuring optimal operation and longevity of systems using R404A refrigerant.