To begin, the recommended oil for refrigerant gas R404A is POE oil. The type of POE oil used for R404A depends on the type of compressor the system employs, its manufacturer, and other considerations.
R404A is frequently used in low-temperature applications because it delivers optimal performance at low temperatures compared to other refrigerants. Additionally, R404A has the unique characteristic of a low discharge temperature, which benefits the compressor’s durability.
Manufacturers of domestic and commercial low-capacity refrigeration systems typically use low-viscosity POE oil. However, it is always advised to consult the manufacturer’s recommendations.
Compressors Commonly Used with R404A
The most commonly used compressor in low-capacity, low-temperature refrigeration systems is the piston-type compressor.
For low-capacity piston compressors operating with R404A, the typical oils used are POE 22 and POE 32.
When performing a complete oil change on an installed compressor and the manufacturer-recommended oil quantity is unknown, it is best to measure the remaining oil in the compressor and add an additional volume, typically 20-30% more lubricant.
The following table provides approximate oil quantities required for piston compressors of different capacities, which can be helpful during oil replacement:
| Compressor Capacity | Approximate Oil Quantity |
|---|---|
| 1/12 HP | 160 cm³ |
| 1/10 HP | 160 cm³ |
| 1/8 HP | 180 cm³ |
| 1/6 HP | 220 cm³ |
| 1/5 HP | 230 cm³ |
| 1/4 HP | 230 cm³ |
| 1/3 HP | 380 cm³ |
| 1/2 HP | 480 cm³ |
| 3/4 HP | 600 cm³ |
| 1 HP | 750 cm³ |
Key Characteristics of POE Oil Used with R404A
Polyolester (POE) oil is highly hygroscopic, meaning it rapidly absorbs moisture from the environment. This absorbed moisture is a major factor in oil degradation.
For instance, leaving a container of POE oil open for more than 12 minutes will result in the oil absorbing significant ambient moisture. Therefore, it is recommended to keep oil cans sealed when not in use or to use an oil pump to minimize exposure.
Issues with Oil Return
If the oil does not return adequately to the compressor, it can lead to insufficient lubrication, causing premature compressor wear and reducing its lifespan. Additionally, excessive oil accumulation in the evaporator can compromise system performance and lower efficiency.
Viscosity Stability Index
When selecting an oil, ensure it has a viscosity stability index (VSI) close to or greater than 100.
The VSI is a numerical measure describing how an oil’s viscosity changes with temperature variations. Oils with a VSI of 100 or higher are considered very stable over a wide temperature range. A VSI below 100 indicates that the oil’s viscosity is more sensitive to temperature changes.
Using high-quality POE oil with a stable viscosity index is essential to maintaining the efficiency and longevity of refrigeration systems operating with R404A refrigerant.
