‘They’ Said It Couldn’t Happen: A Possible Retrofit for Automotive R-134a Refrigerant


When R-1234yf refrigerant was chosen as the low-global-warming replacement for the longtime industry staple R-134a, the consensus being the newcomer refrigerant could never be used in R-134a systems because of its mild flammability. And only the R-1234yf vehicle systems and equipment to service them would meet new flammability safety standards—anti-arcing switches, solenoids and motors and an under-dash evaporator that had to pass severe durability testing to meet the SAE J2842 standard—including salt sprays for corrosion resistance.

R-513A is an azeotropic blend of 56% R-1234yf and 44% R-134a, which is non-flammable; price is far lower than R-1234yf. (Neutronics Inc.)

That meant that although R-134a could be phased out of new-vehicle OEM new systems in favor of R-1234yf, R-134a would have to continue to be available for service long into the future because it was the only choice that was not flammable and had been OEM-approved for automotive air-conditioning (AC). In short, a retrofit of R-134a systems to R-1234yf was not believed to be possible. What alternative was there?

Nothing is forever, and the SAE Interior Climate Control Standards Committee (ICCC) has decided to “take a look” at a new refrigerant that might enable retrofit if regulatory agencies approved. What is this “new refrigerant”—and how was it previously overlooked?

Is higher global warming acceptable?

The new refrigerant is designated as R-513A and its global warming potential is 573, far higher than the worldwide accepted limit of 150 for new auto A/C refrigerants, which explains why it initially was skipped for OEM use.

But that 573 number still is less than half of R-134a’s 1300 (measured using the same Assessment Report 5 data), so as a retrofit it would markedly reduce the global-warming potential of R-134a systems. What’s appealing is that the industry knows it can be used to replace R-134a because Chemours, one of the two producers of R-1234yf and R-513A (branded Opteon XP-10), said so. However, the company doesn’t recommend it as an automotive A/C replacement.

The other source of R-513A is Honeywell, branding the blend as Solstice R-513A.

If not as an automotive A/C refrigerant, what is it for? The manufacturers say it is suitable for new and retrofit applications that were engineered for R-134a, but the application list leads with commercial refrigeration uses that include air conditioning, water and other chillers.

If R-513A ould be applied as a retrofit for automotive A/C, it could reduce the future global-warming potential of hundreds of millions of existing motor vehicles by more than half. That could be appealing to regulatory agencies—and there are reports that European regulators are seriously considering it. Moreover, European equipment makers already have shown R-513a-compatible recovery/recycle/recharge machines, although nothing has been promoted in the U.S.

Might some environmentally-aggressive U.S. agency such as the California Air Resources Board—and the expanding group of other states whose agencies follow the California lead—be interested? With that as a background, SAE International’s ICCC made its “take a look” decision.

R-513A pressure-temperature relationship is close to R-134a and R-1234yf, but is it close enough for retrofit R-134a systems without modifications? (Chemours)

Tradeoffs, of course

The pros:
  • R-513A is an azeotropic blend of 56% R-1234yf and 44% R-134a, which means it does not separate into those two components during operating temperatures and pressures—it basically behaves like a single chemical refrigerant with a pressure-temperature curve close to R-134a.
  • Most important: mixed in the R-513A ratio, R-1234yf is not flammable, so using the existing components of an R-134a system is not an issue.
  • Further, because of its R-134a content, R-513A is far less expensive than pure R-1234yf. It is available at a full U.S. retail price of $750 for a 30-lb (13.6-kg) tank in the U.S., or about $25 lb., much less than half the price of R-1234yf (although much higher than R-134a).

Is the environmental benefit worth it? That would be for regulatory agencies to decide, of course, but worldwide environmental moves, like the Kigali Amendment to the Montreal Protocol that is up for ratification, are pressing for sharp reductions in use of high-global-warming chemicals, particularly refrigerants. Like the two refrigerants in its blend, R-513A has zero ozone layer depletion potential.

It would appear that R-513A could be serviced with repurposed machines designed for/released for R-134a, although revision of charging specifications would likely be necessary.

The cons:
  • Although the pressure-temperature relationship between R-513A and R-134a is close, it isn’t quite the same, and the blend has a slightly higher mass flow rate. In particular, at 32° F (0° C), there is nearly a 4 psi (28 kPa) pressure difference (the R-513A number is higher), so if the system is using a pressure control, a retrofitted system might suffer from icing of the evaporator (moisture condensing on evaporator tubing and fins and freezing), which would stop the cooled airflow.

Most modern R-134a systems, however, use thermistors for system control, which would obviate this issue; the small number of pressure-controlled systems still in use might require installation of a new pressure switch for a retrofit. If as is common, however, the pressure switch is mounted on an under-hood Schrader-type (tire-like) valve, adapting for R-513A would be a simple job, although it would add to the overall cost.

  • Commercial refrigeration compressors use electric motors, so polyol ester (POE) oil is the recommended lubricant for protection of motor windings with R-513A. However, if preferred for retrofit, a poly alkylene glycol (PAG) oil as used in most belt-driven automotive A/C systems is likely to also be acceptable.
  • Other pressure-related issues could arise for some automotive A/C R-134a systems, including operation of condenser fans and any other high-pressure-side controls if used. Or testing R-134a systems might determine that any effect of the change on real-world A/C operation is minor and tolerable within the range of what happens as pressure-based controls drift through their operating life. The R-134a expansion valve is in a similar category. As the Chemours retrofit document notes: “Opteon™ XP10 has slightly higher mass flow rate than R-134a but should be within the usable range of a properly sized and installed R-134a expansion device.”

R-134a began appearing in automotive A/C systems starting in late-1991 and was virtually across the board 3-4 years later. So almost the entire on-the-road vehicle fleet through to 2015 uses it, making the thought of a lower-global-warming replacement of obvious appeal. Naturally, retrofit would only apply to R-134a systems that have leaked out their refrigerant charge.

Thermodynamic properties of R-513A all are reasonably close to R134a except the global warming potential, which is 573 vs. 1300. (Chemours)

EPA regulations require safety, toxicity and environmental risk assessment and then subsequent approval of any replacement refrigerant for automotive A/C. Also mandatory are specific fittings to prevent cross-contamination, so R-513A would be subject to these conditions before it could be used. And because it is a refrigerant that would be used in an existing system, refrigerant identification would be necessary—meaning a new identifier would be required. So any U.S. regulatory adoption of R-513A for R-134a systems would be a multi-step process.