Refrigerants, Global Warming Potential, R-1234yf, and R-744
Refrigerants are working fluids that absorb and release heat as they circulate through an air-conditioning or heat-pump system. Global warming potential (GWP) is a separate climate metric for comparing the warming effect of a released gas with the same mass of carbon dioxide over a stated time horizon.
Main terms
- GWP: the comparison usually uses a 100-year horizon, with carbon dioxide assigned a value of 1. GWP describes the climate effect of an emission; it is not a measure of cooling output, energy efficiency, operating pressure, toxicity, or flammability. U.S. EPA — Understanding Global Warming Potentials
- R-1234yf: also called HFO-1234yf, this is a fluorinated refrigerant used in mobile air-conditioning systems. The U.S. EPA classifies it as mildly flammable and requires system-specific safety measures and service fittings. U.S. EPA — Acceptable Motor-Vehicle Refrigerants and Their Impacts
- R-744: this is the refrigerant designation for carbon dioxide. Its GWP is 1 by definition of the comparison, but vehicle systems using it operate at substantially higher pressure than common fluorinated mobile-air-conditioning systems and require pressure- and leak-specific engineering and service equipment. U.S. EPA — Acceptable Motor-Vehicle Refrigerants and Their Impacts
Why the labels are not interchangeable
R-1234yf and R-744 require different compressors, components, fittings, controls, safety provisions, and service procedures. The correct refrigerant is the one specified on the vehicle label and in manufacturer service information; one must not be substituted for the other.
European mobile-air-conditioning rules prohibit fluorinated greenhouse gases with GWP above 150 in new vehicles placed on the EU market, but they do not mandate one particular refrigerant or system. European Commission — Mobile Air-Conditioning Systems
A lower refrigerant GWP does not by itself make the complete HVAC system more efficient. Compressor design, heat exchangers, circuit architecture, controls, ambient conditions, heating or cooling mode, and operating temperatures determine whole-system performance.
For refrigerant circuits and their role in an EV's thermal system, see Climate systems in electric vehicles.