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This paper presents experimental data from an investigation of an R744 dual evaporator system for automobile applications in a breadboard laboratory. Several expansion devices combinations were investigated, focusing on comparing fixed area and controlled area expansion devices. The role of an accumulator in an R744 dual evaporator system is demonstrated by experiments conducted with a prototype accumulator in which the outflow of liquid R744 and oil is controllable. Contrary to a conventional single R744 evaporator system, the refrigerant outlet qualities in a dual evaporator system are not fixed by the accumulator inlet/exit quality in steady state. An accumulator in an R744 dual evaporator system only guarantees that the quality of the mixed flow downstream of the evaporators has the same quality as the inlet/exit quality of the accumulator.

This paper presents one possible control strategy for a transcritical R744 automotive air conditioning system. The controller is developed for systems using clutch cycling, variable displacement, and variable speed compressors. The controller adjusts the high side pressure, blower speed, reheat, and modulates the compressor to achieve its goal. Test data is presented to support the claims and assumptions made and develop the controller.