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Automotive climate control systems are typically equipped with either an orifice tube or a thermostatic expansion valve. The two devices behave differently especially during cycling operation. The variable restriction of the thermostatic expansion valve delays the refrigerant migration when the clutch is disengaged and allows a faster redistribution when the clutch is engaged. The effect of cycling on the performance of two climate control systems, one with a short-tube orifice, and the other with a thermostatic expansion device, was investigated. The cycle period was varied from 10 seconds to 6 minutes. The test results show the change in moisture removal rate, latent capacity, sensible capacity, energy consumption, and coefficient of performance due to cycling. It is shown that the penalty in energy consumption due to cycling depends on the cycle period.

As a potential replacement to traditional automotive R134a direct expansion (DX) systems, a secondary-loop system allows for the usage of flammable but low-GWP refrigerants such as propane (R290). However, as the secondary-loop system has an additional layer of thermal resistance, the cycle's transient behavior and cabin thermal comfort during pull-down and various driving cycles may be different from traditional DX systems. This paper presents a Modelica-based model to simulate both steady-state and transient operation of automotive secondary-loop systems. The model includes a lumped cabin component and a secondary-loop automotive air-conditioning system component. The air-conditioning system component consists of a condenser, a compressor, an expansion device, a coolant plate type heat exchanger, a coolant to air heat exchanger and a coolant pump. The developed model was validated against both steady-state and transient experimental data for an R290 secondary-loop system.