Which refrigerants are considered very high-pressure refrigerants?

Very high-pressure refrigerants are categorized as those with higher pressures at which they operate, particularly during both their saturation and operation. The group consisting of R-13, R-23, and R-503 fits this definition well.

R-13 and R-23 are noted for their particularly high pressure; R-23, for example, is commonly used in low-temperature refrigeration applications and operates at high pressures even at low temperatures. R-503, originally derived from a mixture of R-12 and R-13, was also designed for applications requiring higher pressure and colder temperatures.

While R-12 and R-134a, R-22 and R-410A, and R-404A and R-407C are all refrigerants utilized in various applications, they are categorized differently based on their pressure characteristics. For example, R-410A is considered a high-pressure refrigerant but not as high as those in selection C. R-404A and R-407C combine various blends but do not reach the same pressure extremes as R-13, R-23, and R-503.

Hence, the correct identification of R-13, R-23, and R-503 as a set of very high-pressure refrigerants