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This paper describes the performance of a transcritical R744 a/c system for a typical compact car. The prototype was designed to have heat exchanger dimensions, face velocities and air-side pressure drops nearly identical to conventional R134a systems. Heat exchangers are made of flat aluminum extruded multiport tubes; the 21 cc compressor is of swash plate design, and the system can be controlled by either a needle valve or a backpressure valve. Test matrices are defined for the purpose of developing component and system simulation models, as well as supporting data-to-data comparisons at normal, seasonal and extreme operating conditions. The design of experiments and test facility are also discussed. Results are presented for the R744 system operating in both steady state and cycling modes.