What the future holds for automotive refrigerants is uncertain, but changes are coming. At some point down the road, R-134a refrigerant will likely be replaced by one or more alternative refrigerants. The question now is which one?

The Europeans have decided to phase out R-134a in new vehicles starting in 2011, with a complete phase-out by 2017. The European rules require any new refrigerants must have a global warming potential of less than 150.

Though R-134a poses no danger to the ozone layer if it escapes into the atmosphere, it is a "greenhouse gas" with a fairly high global warming potential of 1300 (compared to 1 for carbon dioxide, which is nature's own greenhouse gas). A leak that allows only an ounce or two of R-134a to escape into the atmosphere may not seem like a big deal, but over time it all adds up, especially when you multiply small leaks times the hundreds of millions of vehicles that now share planet Earth with humanity.

According to November 2006 report by the Energy Information Administration, vehicles in the U.S. leaked 50.8 thousand tons of R-134a into the atmosphere, equivalent to to over 66 million tons of greenhouse gases. The emissions are 7% higher than in 2004, and up 273 percent since 1995.

As of 2008, the North American and Japanese auto markers have not decided to replace R-134a with any other refrigerant. But the auto makers are redesigning their A/C systems with the following goals in mind:
* To use less refrigerant. Some newer A/C systems now use only 12 to 14 oz. of refrigerant, which is much less than the 24 to 60 oz. charges that most older A/C systems use. As time goes on, we will see more and more of these low capacity A/C systems in new vehicles.
* To reduce refrigerant leakage 50% over the life of the vehicle. This requires using improved seal designs, hoses and o-ring connections.
* To improve cooling efficiency 30% with more efficient condensers, compressors and operating strategies (things like variable displacement compressors that run all the time rather than cycle on and off). Mercedes has this now.
* To reduce the cooling requirements inside the passenger compartment 30% by using reflective coatings on glass, heat reflective paint, and venting the interior during hot weather.
Changes are also being made to reduce refrigerant losses when the A/C system on a vehicle is serviced. The latest generation of refrigerant recovery machines do a better job of removing all of the refrigerant from the system. Older machines can leave as much as 20 to 30 percent of the old refrigerant charge in the system. The residual refrigerant can escape into the atmosphere when the A/C system is opened to replace parts. Some of the newest machines can pull up to 95% of the refrigerant out of the system to reduce the amount of R-134a that escapes into the atmosphere.
Auto makers have also been adding leak detection dye to the refrigerant to make it easier for technicians to detect refrigerant leaks. A leak will leave a telltale stain that glows greenish-yellow or greenish-blue when illuminated with an UV light source. Leaks as small as 1/8 oz. of refrigerant per year can be detected this way.

The Europeans auto makers are taking a different approach. They want future A/C systems to be as environmentally benign as possible. That means no chlorine-containing CFCs such as R-12 or R-22 that cause ozone depletion, an no refrigerants that could add to the global warming problem (which includes R-134a). Any new refrigerants must also be nontoxic and safe, though that doesn't necessarily mean nonflammable.

In an effort to address these issues, the Alliance for Responsible Atmospheric Policy (ARAP) and the U.S. Environmental Protection Agency (EPA) have held a series of annual meetings to discuss and evaluate alternatives to R-134a. The first of these meetings was held in 2003 by the European Commission in Brussels. As a result of that meeting, the European Commission decided to allow carbon dioxide, HFC-152a and other refrigerants as possible replacements for R-134a.

CO2 as an Alternative Refrigerant

When used as a refrigerant, CO2 (which is called R-744) requires extremely high operating pressures (up to 1,800 psi on the high side, and 350 to 400 psi on the low side), compared to 300 to 400 psi on the high side for R-134a. The reason the pressures are so high is because CO2 does not condense in the refrigeration circuit. It remains in the gaseous state. Consequently, the front heat exchanger is called a "cooler" rather than a condenser.

CO2's main attribute is that it has virtually no impact on global warming or ozone depletion. CO2 is also nontoxic in small doses but concentrations over 5% can be lethal. It is also cheap (about $10 for a 20-lb. cylinder) and nonflammable. Numerous test vehicles with CO2 A/C systems hae shown that CO2 does provide cooling performance comparable to R-134a.

SAE is developing service fitting standards for R-744. Leak detection presents a challenge because natural levels of CO2 in the atmosphere may be higher than the amount emitted by a leak from an A/C system. Some type of ultrasound or infrared equipment may be required to find R-744 leaks, but dyes may also work or plain old soap bubbles.

HFC-152a

HFC-152a is almost a straight drop-in substitute for R-134a. The molecule is similar to R-134a except that two hydrogen atoms are substituted for two fluorine atoms. It has similar operating characteristics to R-134a but cools even better. One test in an otherwise unmodified Saturn Ion found that A/C duct outlet temperatures were several degrees C lower with HFC-152a. Fuel efficiency was also up 10% at idle, and 20% at highway speeds. The system typically requires only about two-thirds of the normal charge with HFC-152a and can be used with current desiccants.

An environmental benefit of HFC-152a is that it has a global warming rating of 120, which is 10 times less than R-134a, but still a lot higher than CO2. That is why HFC-152a is currently used in many aerosol products as a propellant. Its main drawback is that it is slightly flammable (Class 2A), but it is not as flammable as propane or most other hydrocarbon-based refrigerants.

The first mobile A/C system to use HFC-152a was unveiled at the Mobile Air Conditioning Society (MACS) Worldwide tradeshow in January 2004; a self-contained unit for off-road construction equipment that featured an oil-driven compressor. Made by Red Dot, the unit may be the forerunner of future HFC-152a A/C systems to come.

Red Dot staff explained that the HFC-152a refrigerant used in the self-contained unit improves cooling capacity, decreases fuel use and helps protect the climate. The new technology also satisfies stringent new regulations proposed by the European Commission. Red Dot staff also said that the HFC-152a system uses new technology that will use hydraulic-driven compressors and secondary loop technology to increase reliability, safety and reduce the amount of refrigerant required.

HFO-1234yf

Another new refrigerant that is being considered is HFO-1234yf. Developed jointly by Honeywell and DuPont, it is being promoted as a possible drop-in replacement for R-134a in both new vehicles and older vehicles, should that become necessary in the future. HFO-1234yf has thermal characteristics that are very similar to R-134a, so no major modifications to the A/C system are necessary. Better yet, HFO-1234yf has a global warming potential of only 4, compared to 1200 for R-134a, allowing it to meet the European requirements for a GWP of less than 150. Existing refrigerant leak detectors can also detect HFO-1234yf if it leaks. But HFO-1234yf is mildly flammable (though less so than HFC-152a), and long term toxicology tests are still underway.

EPA Says It Will Not Restrict R-134a Sales

Sales of R-134a refrigerant will not be restricted, according to a rule that was finalized by the EPA in February, 2004. In a release by the Automotive Parts & Service Alliance (APSA), the EPA had proposed in June 1998 to restrict the sale of the refrigerant to only certified users, but had not finalized the proposal due to opposition from some aftermarket associations, including Automotive Aftermarket Industry Association (AAIA) and Automotive Refrigeration Products Institute (ARPI).

However, MACS agreed with the restriction proposal. In its report to the EPA in May 2002, MACS argued that the release of HFC-134a refrigerant to the atmosphere during service of a mobile A/C system is illegal and detrimental to the environment. With the availability of R-134a to the general public, there has been minimal enforcement related to the venting of refrigerant by consumers who service their own automotive systems or unprofessional service personnel who do not have the federally mandated refrigerant recovery equipment.

The EPA had based its proposed sale restrictions on the issue that car owners converting their vehicle A/C systems to R-134a would vent into the atmosphere any R-12 that remained in the system.

AAIA and ARPI said it opposed the EPA's proposal, and questioned its authority under the Clean Air Act to take such action, focusing on the issue that the restriction would unfairly impact low- and fixed-income individuals who are forced to work on their own vehicle A/C systems for economic reasons.

Update: November 2008

SAE Says HFO1234yf is Best Alternative Refrigerant for R-134a

In a recent press release, the Society of Automotive Engineers (SAE) International Cooperative Research Program (CRP) says HFO1234yf offers "superior environmental performance" for future mobile air conditioning systems that may be redesigned for alternative refrigerants.

The CRP1234-1 and CRP1234-2 programs, launched in 2007, have investigated the safety and performance of the new refrigerant HFO1234yf. Under the direction of the SAE CRP members (who are international experts in this field from OEMs, Tier 1 and 2 Suppliers and independent test facilities), air conditioning system performance, material compatibility and relative risks of HFO1234yf were evaluated. Based on these studies, HFO1234yf was judged to have the lowest risk for use in mobile A/C systems compared to all of the other alternative refrigerants that are currently being evaluated. This is based on the Life Cycle Climate Protection analysis that estimates CO2 Equivalent emissions from automotive A/C usage (as described in SAE J2766).

The study was conducted in response to European Union regulations that will require all new vehicles made for model year 2011 and later to use a refrigerant with a Global Warming Potential (GWP) below 150. Current automotive A/C systems all use R-134a, which has a GWP of 1,430. HFO1234yf has a GWP of only four.