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The subject addressed by this work, currently discussed in Europe following an European Commission inquiry, is the evaluation of the possibility to prevent the MAC (Mobile Air Conditioning) use below 18°C and its benefits in terms of CO2 emissions saving. This strategy, while providing an uncertain fuel consumption saving, has to be faced with basic safety and cabin comfort conditions. The OEMs (Original Equipment Manufacturers) may evaluate to address these concerns by controlling the cabin absolute humidity content. In order to maintain safety it should be acceptable to turn the AC on based on other inputs, such as air distribution modes (defrost or floor/defrost), windshield wiper usage, rear defroster usage, etc. FGA (FIAT Group Automobiles) exploited our proprietary prediction tool to assessing the yearly fuel efficiency that can be achieved in real use by means of the testing results of representative vehicles.

The new F-Gas European Union (EU) Legislation requires car manufacturers to design their vehicles for application of low Global Warming Potential (GWP) refrigerant gasses. Low GWP substitutes to R-134a for Mobile Air Conditioning (MAC) application have to be assessed based on their potential for human exposure in terms of toxicity and flammability. Among the current potential candidates, the present paper deals with the flammability risk assessment of HFO-1234yf. This joint DuPont and Honeywell proposal is a Hydro-Fluoro-Olefin, 2,2,2,3 Tetrafluoroprop-1-ene.

The current A/C system performance prediction codes usually describe the TXV behaviour in terms of SH dependence on the evaporation pressure. The data currently issued by TXV suppliers give the maximum outlet evaporator pressure values at 0 °C and 10 °C outlet evaporator temperature (Fig. 1).