The European Union is expected to outlaw the use of the hydrofluorocarbon R134a as the air conditioner refrigerant used in new cars sold after 2011.
Carbon dioxide, though a greenhouse gas, is the leading replacement candidate. It's also called C02.
R134a is 1,300 times more damaging to the earth's ozone layer than CO2-based refrigerant, scientists say.
How it works
An inexpensive natural byproduct, CO2-based air conditioners use a closed system requiring a smaller amount of gas -- as little as one-fifth -- compared with conventional systems.
CO2 technology also involves a heat-pump operation, providing auxiliary warmth for the passenger cabin and better control of glass fogging.
Where to find it
The Toyota Kluger V FCHV-4 hydrogen fuel cell vehicle incorporates a CO2 prototype system from Denso Corp. with an electric heat pump.
Last year Delphi Corp. demonstrated CO2 air conditioning in an Alfa Romeo 147. Visteon Corp. and Behr GmbH & Co. KG say their CO2 systems will be ready by 2009.
The system's complexity and the cost of materials are the main drawbacks. Above 104 degrees Fahrenheit, the system needs an additional interior heat exchanger, which would add cost.
There also are infrastructure issues such as providing service and maintenance equipment.
CO2 systems also must include a way to warn passengers if the gas enters the car because too much CO2 can be poisonous.
Behr, Delphi, Denso, Modine Manufacturing Co., Valeo SA and Visteon.