Experiments were carried out on a R134a vapour ejector refrigeration system to study the influence of ejector configurations and operating conditions on its performance at critical mode. The influence of boiler temperature, which represent the solar energy collection temperature and that of evaporating temperature, which denotes the cooling load temperature, have been studied. Coefficient of performance was obtained for evaporating temperatures in the range of 275 K to 285.5 K and boiler temperatures between 338 K and 363 K. It has been observed that ejector configuration has significant influence in deciding the operating range and overall system performance.