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Automotive fixed orifice tube (FOT) systems are especially prone to cycling losses due to their clutch cycling operation. Therefore, it is important to better understand the dynamics of the refrigerant and oil migration during transient events such as cycling and start-up. To measure the refrigerant mass and oil distribution of an automotive R134a FOT breadboard system, two ball valves around each component are added. By simultaneously closing the valves, the refrigerant and oil is trapped in different sections of the system and can be measured. The transient refrigerant migration during a stop-start transient as well as the refrigerant mass distribution as a function of system charge at steady state operation is presented. A transparent accumulator and transparent tubes at the inlet and outlet of the accumulator are used to visualize the flow of the refrigerant. High speed video snapshots are presented for the first seconds after the start-up.

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.