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As an alternative refrigerant for CFC-12, HFC-134a is the best choice in automotive air conditioning system. Refrigeration cycle characteristics using HFC-134a have been previously reported, but most of those papers were confined to the differences of basic system performance between CFC-12 and HFC-134a. So this paper emphasized the analysis on functional components. As a result, we have introduced the differences of refrigeration cycle characteristics which had not been acquainted well by now.

A piezoresistive semiconductor pressure sensor that can be measure high pressure upto 3.5 Mpa within ±1% error of FS (Full Scale) has been developed; it is suitable for use in automotive electronic control systems such as suspension, transmission, anti-skid brakes and air conditioners. This pressure sensor has a silicon diaphragm in which piezoresistive elements are diffused and form a wheatstone bridge circuit to newly developed to achieve high accuracy. High resisting pressure of more than 10 MPa (300% of rated pressure) and high sensitivity of more than 100mV/V supply ·3.5 MPa were achieved by the optimum designe of diaphragm shape.