Production of chlorofluorocarbons (CFCs) is being banned due to environmental concerns regarding ozone depletion. All CFCs are anticipated to be out of production by the year 2000. This ban has prompted the need for converting existing systems to use atmospherically safe refrigerants or replacing the systems altogether with environmentally safe alternatives.This paper documents an analytical study initiated on the E-2C aircraft program to assess requirements for converting the existing vapor cycle system from R-114 to R-134a. The effort focused on determining the maximum cooling capability readily achievable with the new fluid within the present system volume, and identifying the associated changes in vapor cycle system weight and power required to maintain at least the existing system capacity. Particular emphasis was placed on avoiding changes to the ram air scoop to eliminate flying qualities impact. A vapor cycle performance code was developed to obtain maximum system cooling capacities at the design condition for several component configurations. Parametric analyses were also used in assessing required compressor characteristics over a range of cooling loads and compressor efficiencies.