This paper describes the design of a steam jet ejector and its validation. The ejector formed part of an experimental ejector cycle designed to be installed in a small motor vehicle to provide air-conditioning. The coolant and/or exhaust heat from the engine could be used to drive the ejector cycle. The design of the ejector was derived from guidelines published in the ESDU series. The ejector system was then manufactured and tested on a laboratory controlled test rig that simulated conditions present in a smalt motor vehicle. Computational fluid dynamics (CFD) analysis was performed on the ejector to determine its expected performance. The results obtained through CFD analysis were compared with the practical test data for a range of operating conditions. Comparisons were made using the mass flow ratio of the ejector. The coefficient of performance (COPR) of the system is presented for all operating conditions tested.