was gathering info and came across this
some cutting and pasting done
Future A/C Systems
the future of mobile A/C systems revealed some interesting information about what’s happening in Europe and how it will impact North America. The Europeans are moving to phase out R-134a as a refrigerant by 2011 because it is on the hit list of gases that contribute to global warming. Most of the European nations signed the Kyoto Protocol that calls for cutbacks in carbon dioxide emissions and the release of other global warming gases. The U.S. did not sign this agreement, so it is uncertain how this will impact us. But within the next five to eight years, the Europeans will probably start introducing higher pressure CO2 (R-744) A/C systems on high-end luxury cars.
Since the thermal property of CO2 is different from current refrigerant, CO2 is especially effective in heating a vehicle compared with the HFC-134 alternative refrigerant used in other automotive air-conditioning systems. In the CO2 system, heating is accomplished by switching to the refrigerant channel so that the refrigerant can be compressed and supplied to the passenger compartment heat exchanger from which it radiates heat. In other automotive air-conditioning systems, a hot engine coolant that has been heated by the engine heat is circulated through the heater core to warm the passenger compartment. Until now, fuel cell vehicles and electric vehicles (EVs) have had the drawback of not providing very effective cabin heating because they lack a heat source as they do not have an internal combustion engine.
The CO2 air-conditioning system uses the same process as ordinary automotive air-conditioners to cool a vehicle. The refrigerant -- in this case CO2 -- is evaporated by a passenger car compartment heat exchanger to absorb heat and cool the vehicle's cabin.
CO2 is a naturally occurring, non-flammable refrigerant and is more environmentally friendly than the HFC-134a alternative refrigerant. The new CO2 system can help to reduce the amount of CO2 discharged from factories because CO2 waste from factories can be reused for use in the system.
The implementation of the new air-conditioning system has been made possible in part by the successful development of a compact, lightweight compressor capable of withstanding the high temperature and high pressure needed to compress CO2. Another contributing factor is the successful development of a heat exchanger capable of withstanding the high pressure and temperature of the highly compressed CO2 gas supplied from the compressor.
Moreover, the power loss that ordinarily occurs in a small car when the air conditioner is operated while driving can be reduced with this air-conditioning system through suitable control of the compressor torque. Further development work is now under way with the aim of using this CO2 air-conditioning system on vehicles powered by a gasoline engine.
The advantage of using CO2 as a refrigerant is that there’s no net increase in global warming gases. The drawback is that a CO2 system operates at extremely high pressure - 1,500 psi on the low side and 2,500 psi on the high side. This requires much stronger tubing and poses a hazard to service technicians.
Another alternative refrigerant that is being considered is HFC-152, which is slightly flammable. It may be used in a "secondary loop" A/C system that uses a heat exchanger to transfer cooling from the refrigerant in the engine compartment to ordinary antifreeze coolant that is circulating into the passenger compartment.
In the near future, we will see even more electronics in A/C systems, including more computer-controlled variable-displacement compressors, electronic orifice tubes and expansion valves, and electric-driven compressors in vehicles that have an idle shut off system to reduce fuel consumption
http://www.aa1car.com/library/newac2k.htm
