In the majority of automotive air conditioning systems, the compressor continuously cycles on and o to meet the steady-state cooling requirements of the passenger compartment. Since the compressor is a belt-driven accessory device coupled to the engine, its cycling rate is directly related to the vehicle speed. The refrigeration system's losses increase with increasing vehicle speed and thus with increasing compressor cycling. This paper identi®es and quanti®es individual losses in an automotive vaporcompression refrigeration system during compressor cycling. The second law of thermodynamics, in particular, nondimensional entropy generation, is used to quantify the thermodynamic losses of the refrigeration system's individual components under steady driving conditions at idle, 48.3 kph (30 mph), and 96.6 kph (60 mph). A passenger vehicle containing a cycling-clutch ori®ce-tube vapor±compression refrigeration system was instrumented to measure refrigerant temperature and pressure, and air temperature and relative humidity. Data were collected under steady driving conditions at idle, 48.3 kph (30 mph), and 96.6 kph (60 mph). A thermodynamic analysis is presented to determine the refrigeration system's performance. This analysis shows that the performance of the system degrades with increasing vehicle speed. Thermodynamic losses increase 18% as the vehicle speed changes from idle to 48.3 kph (30 mph) and increase 5% as the vehicle speed changes from 48.3 kph (30 mph) to 96.6 kph (60 mph). The compressor cycling rate increases with increasing vehicle speed, thus increasing the refrigeration system's losses. The component with the greatest increase in thermodynamic losses as a result of compressor cycling is the compressor itself. Compressor cycling reduces the compressor's isentropic eciency, and thus the system's thermodynamic performance. The individual component losses of the refrigeration system are quanti®ed. The redistribution of these losses is also given as a function of increasing vehicle speed (i.e. increasing compressor cycling). At 96.6 kph (60 mph), the thermodynamic losses, based on the ratio of entropy generation to entropic load, are 0.22, 0.10, 0.07, and 0.02 in the