Which of the following is NOT a common refrigerant used in HVAC systems?

The choice of refrigerant plays a vital role in HVAC systems, affecting efficiency, environmental impact, and regulatory compliance. R-12 is not commonly used in modern HVAC systems, primarily because it is a chlorofluorocarbon (CFC) that has been phased out due to its harmful effects on the ozone layer. The Environmental Protection Agency (EPA) instituted regulations that significantly restrict the use of CFCs, leading to a decline in the use of R-12.

In contrast, R-410A, R-22, and R-404A are commonly used refrigerants today. R-410A is a popular choice in newer systems as it does not deplete the ozone layer and has a higher efficiency rating. R-22 was widely used in older systems but is also being phased out due to environmental concerns, and its production is being gradually reduced. R-404A is often used in low-temperature refrigeration applications and is preferred for its efficiency in commercial refrigeration settings.

Understanding the transition from CFCs and the adoption of more environmentally friendly alternatives is crucial for anyone studying HVAC practices. This context highlights why R-12 is considered obsolete in today's HVAC landscape.