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Many drivers turn on the air conditioning in their cars without ever giving much thought to how the system works. That is, unless your A/C starts to smell bad or worse yet stops working properly. Until then, it’s easy to assume that a car’s air conditioning unit is one of those systems that engineers have mostly perfected over the decades. However, behind the scenes, it’s a very different story. Scientists have been working for years to try and cut down the amount of emissions that A/C systems generate, and it turns out that the industry’s previous efforts might not quite have been as successful as it was initially hoped.
The culprit is the refrigerant that’s used in many modern systems. It was supposed to be a more environmentally-friendly alternative to the previously used chemicals, but new studies have cast doubt on that idea. This isn’t the first time that this has happened either; manufacturers have already changed the refrigerant that they used twice before, and now it looks like they’ll have to do it again.
Early automotive A/C systems mostly used a refrigerant called R-12. It was synthesized by researchers who were trying to create a stable, non-toxic substance to replace the litany of potentially hazardous chemicals that the first commercial refrigerators had used. The new chemical proved to be very effective and just as stable as hoped, but scientists later found that it was contributing to the loss of the Earth’s ozone layer. In response, automakers switched to a new refrigerant, R-134a, in the 1990s.
Today’s main refrigerants are still problematic
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This initial change was seen as an improvement; R-134a, which is also called HFC-134a, didn’t contribute to ozone depletion. However, it was part of the chemical group known as per- and polyfluoroalkyl substances, or PFAS. They’re sometimes referred to as “forever chemicals,” because they can cause long-lasting contamination when they’re released into the environment. Research about the full effects of these chemicals is ongoing, but studies have shown that areas with high levels of PFAS contamination in drinking water have seen higher instances of some types of cancer, as well as other diseases.
R-134a is also a greenhouse gas with a high global warming potential (GWP). As the use of R-134a-based A/C systems increased, so did the concentration of R-134a in the atmosphere. This finding prompted European authorities to ban the use of R-134a refrigerant in new car’s A/C systems in 2017, with manufacturers instead replacing it with R-1234yf (also called HFO-1234yf). This new refrigerant has a much lower GWP, but now new research has suggested that it pollutes the environment in a different way.
A 2026 study published in the journal Environmental Science and Technology Letters found that R-1234yf can break down into trifluoroacetic acid (TFA) in the atmosphere at a significantly higher rate than R-134a. According to the findings, R-1234yf produces between 3.6 and 10.3 times as much TFA as R-134a. TFA is a type of PFAS that scientists are particularly worried about, since it’s been linked to liver disease and developmental issues with unborn children. It’s also extremely long-lasting, with scientists warning that its accumulation in the environment is effectively irreversible.
Some of the newest refrigerants aren’t actually new
With R-1234yf being a lot less eco-friendly than scientists initially thought, the clock is ticking for manufacturers to find alternatives yet again. Some are already beginning to phase out R-1234yf, with several Volkswagen Group brands switching certain models to R-744 instead. This latest refrigerant is more commonly known as carbon dioxide (CO2).
This is far from a new idea — carbon dioxide’s suitability as a refrigerant has been known for decades, and it drew a lot of attention in the late 1990s when researchers were trying to find alternatives to R-134a. At the time, carmakers like GM opted not to use R-744, in part due to the fact that it needs to operate at significantly higher pressure than R-134a.
Volkswagen came across the same problem, but chose to use it anyway because R-744 brings a couple of key benefits when it’s used in EVs. Battery packs can deliver less range when they’re cold, and R-744 is particularly good at transferring heat in colder operating temperatures. In turn, that helps boost the car’s range, which is a big enough benefit to offset the inconvenience of the high-pressure system.
Another refrigerant that’s attracting interest is R-290, which is propane. It has a low GWP and it’s efficient, but the compromise is that it’s flammable. Still, it’s considered less polluting than today’s main refrigerants, and a report by IDTechEx suggests that demand for both of these alternatives is set to increase significantly over the coming years as manufacturers start to make this latest switch.