At i+1th expansion valve opening step, the ith pressure was subtracted and the result was defined as DP and presented in Fig. 11. As seen in the figure, the pressure change near the highest COP region of gas-cooler is 3.3 times larger than the pressure change of evaporator. However, it is obvious that the pressure change of evaporator gives substantial influence on the calculation of compressor work change. To neglect the evaporator pressure term in differential equation, the order of the value should be lower than that of the other terms but the degree of order of pressure change of evaporator does not seem smaller than that of gas-cooler. As a result, the negligence of evaporator pressure change would yield some error of the controller. In comprehensive aspects, neglecting evaporator pressure causes underestimation of increment of specific compressor work and it compensates underestimation of specific cooling capacity increment. Hence, in this situation, the negligence of evaporator pressure is helpful to reduce the bias caused by the underestimation of increment of cooling capacity. Nevertheless, in the final heat rejection control problem, it is necessary to devise a method which can consider the pressure change of evaporator and it is left to an assignment for future researches