While the mass of refrigerant contained in a vapor compression cycle has a significant effect on the cycle's power consumption, conventional cycle architectures cannot optimize energy efficiency by varying the mass as ambient conditions and operational requirements change. This paper proposes a new system architecture that allows the refrigerant mass circulating in the system to be modulated over time in response to the operating conditions. This new architecture is developed with a set of dynamic cycle simulations that facilitate the specification of the mass in the cycle, and which eliminate numerical errors that can cause nonphysical fluctuations in the total mass. Controls that optimize the mass in the cycle as a function of the operating conditions are also incorporated into the overall system, allowing it to be constructed without the addition of new sensors. Gains in the coefficient of performance for this new system exceeding 10% over cycles with a fixed refrigerant charge are demonstrated.