Which refrigerant is currently illegal to use in new vehicles?

The refrigerant that is currently illegal to use in new vehicles is R-134a. This ban is primarily due to its global warming potential and the push towards more environmentally friendly alternatives. Over the years, regulations have tightened around refrigerants that contribute to climate change. As a result, the automotive industry has shifted toward using refrigerants with lower environmental impacts, such as R-1234yf, which is now more commonly used in new vehicle models.

R-12, while phased out for many applications due to its ozone depletion potential, does not apply to new vehicles but rather to older models. R-22 is primarily used in residential cooling systems rather than automotive applications and is also being phased out due to environmental concerns. R-410A is used in residential and commercial air conditioning but is not used in automotive systems, making it irrelevant to this specific question.

Thus, R-134a stands out as the refrigerant that has been replaced under regulatory changes for new automotive applications, emphasizing the industry's commitment to reducing environmental impact.