In this thesis, one of the current control algorithms for the R744 cycle, which tries to optimize the performance of the system by two SISO control loops, is compared to a cost-effective system with just one actuator. The operation of a key component of this system, a two stage orifice expansion valve is examined in a range of typical climate conditions. One alternative control loop for this system, which has been proposed by Behr group, is also scrutinized. The simulation results affirm the preference of using two control-loops instead of one loop, but refute advantages of the Behr alternate control approach against one-loop control. As far as the economic considerations of the A/C unit are concerned, using a two-stage orifice expansion valve is desired by the automotive industry, thus based on the experiment results, an improved logic for control of this system is proposed. In the second part, it is investigated whether the one-actuator control approach is applicable to a system consisting of two parallel evaporators to allow passengers to control different climate zones. The simulation results show that in the case of using a two-stage orifice valve for the front evaporator and a fixed expansion valve for the rear one, a proper distribution of the cooling power between the front and rear compartment is possible for a broad range of climate conditions.