R-1234yf refrigerants for mobile air-conditioning systems have been widely used in passenger vehicles the past several years, but they are just now gaining traction in medium- and heavy-duty commercial vehicles. Environmental policies are driving the shift to R-1234yf, which has a Global Warming Potential (GWP) of <1 compared to R-134a’s GWP of 1,300.

“The significant difference is due to R-1234yf being a hydrofluoroolefin (HFO), a molecule that has a very short-lived atmospheric life,” said Christina Spalding (below), account manager for The Chemours Company, which makes Opteon YF (R-1234yf) refrigerant. “Where hydrofluorocarbon (HFC) R-134a remains in the atmosphere an average of 12 years, R-1234yf’s atmospheric lifetime averages a mere 11 days.”

As of November 2021, R-1234yf has been listed as a proposed alternative under the EPA SNAP (Significant New Alternatives Policy) Program. “In anticipation of the publication of the final ruling, many OEMs are now actively developing systems using R-1234yf,” she said. Also driving this shift is the mandated HFC phasedown defined by the AIM (American Innovation and Manufacturing), which began January 1, 2022. Spalding shares additional insights with SAE Media in the following Q&A.

Why has there been such a delay between passenger and commercial vehicles employing the new refrigerant?
R-1234yf was listed as an EPA-approved mobile refrigerant for new vehicles under SNAP in 2012. R-1234yf usage was accelerated with signature of the Kigali Amendment to the Montreal Protocol in 2016. This multinational agreement pledged the phasedown of certain HFCs like 134a. Though the U.S. has not signed it, adoption of Kigali in the EU compelled automakers to develop R-1234yf-based systems. The final driver in the U.S. for the passenger-vehicle transition to R-1234yf was the 2015 EPA SNAP rule 20 prohibiting 134a in new light-duty cars and trucks as of model year 2021.

OEMs prioritized the SNAP listing [rule 24] for R-1234yf in new off-highway heavy-duty vehicles due to the desire to manufacture vehicles in the U.S. and ship them to Europe. There has not been similar motivation in the on-highway medium- and heavy-duty truck vehicle classes until the passage of the AIM Act, which defines the timeline by which the OEMs will need to reduce R-134a usage.

Have any regions adopted R-1234yf faster than others?
Although R-1234yf is being used globally by a majority of key OEMs in light-duty automotive, the transition to the commercial/off-highway segment has not been widespread across other regions. However, the recent SNAP ruling, in combination with the AIM Act in the U.S., positions R-1234yf as the preferred replacement for R-134a for global manufacturers.

Any specific challenges to applying R-1234yf to commercial/off-highway vehicles?
The thermal performance, non-toxic chemistry and stability are nearly the same between R-1234yf and R-134a. The primary difference between the two is R-1234yf being slightly more flammable. ASHRAE classifies R-1234yf as a “mildly-flammability” fluid (A2L); R-134a carries an A1 safety classification due to its lower flame propagation.

The risk characteristics of the increased flammability of R-1234yf were evaluated in the SNAP ruling, but this difference prevents the refrigerant from being a direct drop-in replacement. In addition, the system components need to be rated for R-1234yf before the refrigerant can be used. The SNAP ruling recommends SAE safety standards J639, J1739 and J2844 for the applicable use cases.

Are there any differences in the refrigerant system itself?
There aren’t any specific new types of components required. However, it is critical to ensure that system components are rated for R-1234yf and that the appropriate safety standards are followed. In addition, it is strongly encouraged that users include an internal heat exchanger (IHX). Following this best practice will help to ensure cooling capacity of the evaporator can be met at all desired operating conditions given the slight differences in properties between the two refrigerants.

Any other benefits beyond environmental?
R-1234yf has a higher vapor density than R-134a. Higher vapor density enables the use of a smaller compressor, reducing the system’s energy consumption.

Does electrification impact the outlook for refrigerants moving forward?
The properties and regulatory fit of HFO-1234yf make it an ideal base molecule for electrified heavy-duty vehicles. Because EVs present unique challenges in cabin heating and battery cooling, innovators such as Chemours are constantly evaluating options to tailor the benefits of R-1234yf for electrified applications.