When the 2017 E-class debuts next year, Mercedes will market the hell out of its self-driving capabilities and electronic safety aids. Nary a primetime TV ad will detail a decidedly unsexy yet important feature: The new air-conditioning system.
Mercedes will be first to market with a carbon-dioxide refrigerant, an eco-friendly alternative that promises greater fuel economy, quicker cooling, and faster defrosting. While this sounds counterintuitive as governments call for slashed vehicle CO2 emissions, the world’s most abundant greenhouse gas is actually the least harmful choice for A/C units in terms of what climate scientists call global-warming potential (the relative level of atmospheric heat that gases trap over 100 years compared to CO2). Among the synthetic hydrofluorocarbons in use today, the common R134a refrigerant has a global-warming potential 1430 times that of CO2. Yet compared to the chlorofluorocarbons damaging the ozone layer before their ban in 1996, R134a was and is a huge improvement.
But emissions laws are only getting tougher. It’s why the European Union has banned R134a refrigerants for new cars starting in January 2017. The U.S. is requiring the same change for the 2021 model year. All automakers must switch to alternative gases, but only European versions of the 2017 E-class and S-class have leaped all the way to CO2.
Estimates vary, but CO2 refrigerant—known in HVAC parlance as R744—is yet another trick automakers can wield to increase efficiency and improve cooling performance, much like the dual benefits of more power and greater efficiency delivered by direct fuel injection. But CO2 is a notoriously difficult gas to stream within existing A/C systems. To sustain a required pressure of more than 1450 psi, roughly 10 times the level of today’s R134a refrigerant, Mercedes had to redesign everything—all-new compressors, hoses, seals, you name it. It also has to ensure there’s no leaking CO2 and train service technicians on how not to asphyxiate themselves. And, yes, that’s all very expensive.
The 2017 E-class in all of its camouflaged glory.
And so much of the industry is instead moving to R1234yf, a hydrofluoroolefin that breaks down in the atmosphere after just a few days and has but four times the level of global-warming potential as CO2. It’s way cheaper, widely available, and won’t require massive bouts of reengineering. But unlike R134a and CO2, R1234yf is potentially flammable. After Daimler released test results of R1234yf bursting into flames in 2013, it refused to continue using the refrigerant and recalled cars that had the gas onboard. Since then, all the German automakers “have decided to concentrate on and complete the development of air-conditioning systems that are suitable for the use of R744,” according to the German Association of the Automotive Industry, which completed a technical standard for CO2 usage. The Society of Automotive Engineers hasn’t yet adopted a CO2 standard, although it will be “considered and evaluated,” program manager Gary Pollak told us.
“My observations are that R744 needs additional system design development before it is cost effective in the mainstream,” Pollak said. “R1234yf use systems are already viable.”
Daimler also has reversed course on R1234yf to temporarily satisfy emissions regulations across its entire lineup, but not without its typical hyperfocus on safety. The company is developing special crash structures to keep the refrigerant separate from the engine compartment and is installing a system that, upon a crash, will release argon gas to cool the “relevant hot spots” to prevent a fire.
Until this refrigerant debate chills and we see some data from one of these Euro-spec Benzes, we’re not taking bets on better cabin comfort or fuel economy. But it’s nice to see automakers fighting over subtle improvements that every driver may one day feel.
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