The Europeans are paving the way, driving alternative refrigerant technology. The European “F-Gas” rules have declared that R-134a must be replaced with a refrigerant that has a significantly lower global warming potential (a rating no higher than 150 GWP). The phase-out on new vehicles must start in 2011 and be complete by 2017.
The European decision to phase-out R-134a does not apply to US or Asian vehicle manufacturers outside of Europe, but it does apply to any vehicle manufacturer who wants to sell cars or trucks in Europe regardless of where the vehicles are built. Consequently, if the Europeans require a new refrigerant for all of their vehicles, it will affect vehicle manufacturers worldwide and eventually the U.S. aftermarket.
Vehicle manufacturers don’t want to build different A/C systems for different world markets. A common refrigerant is the most economical. But
it’s not as simple as it sounds. One reason is that any one of several alternative refrigerants may work. There are advantages and disadvantages for each, and it is possible that different vehicle manufacturers may come to different conclusions as to which one is the best to use.
One alternative refrigerant being considered is HFC-152a. It has a GWP rating of 140, which meets the European requirements. HFC-152a has cooling characteristics very close to that of R-134a, and could probably be used as a direct substitute for R-134a with few if any modifications. But HFC-152a has one serious drawback: it is flammable. If the refrigerant leaks into the passenger compartment, it could explode. The EPA currently bans flammable refrigerant for mobile A/C use (except in truck refer trailers), and many states also have laws that prohibit its use.
One possible solution to the flammability problem with HFC-152a is to add a leak sensor inside the vehicle to warn the passengers and open the windows if a leak occurred. Another approach is to redesign the A/C system so that it uses a “secondary loop” to keep the flammable refrigerant in the engine compartment and out of the passenger compartment. With this approach, the refrigerant circulates through an intermediate heat exchanger and chills a liquid (probably a water/antifreeze mixture) that then flows through the HVAC unit inside the vehicle. A recent report from the U.S. EPA says this approach meets its safety criteria, while also being energy efficient.
Propane is another possibility, but is considered to be much too flammable for automotive applications (though it is used in the refrigeration units on truck trailers, and even in some European household refrigerators).