This paper compares the system performance for two representative capacity control schemes, hot-gas bypass and variable speed compressor in an oil cooler for machine tools. An empirical linear first-order model of each controlled system was obtained from experiments by imposing a stepwise control signal to each actuator of the system. General proportional-integral controllers are designed based on the empirical transfer function models in order to control the target temperature of the oil cooler system. The experiments of starting and thermal load change were conducted to compare their control performance with each other. Especially, coefficient of performance (COP) of the two control schemes under the partial load state was also analyzed in detail. From the analyses of experimental results, the control performance of the target temperature in the two control schemes had almost the same control accuracy of ${pm}0.1^{circ}C$ at steady state. However, the COP of a variable speed compressor was as many as five-times greater than that of hot-gas bypass in comparable minimum partial load state of 0.5 kW.