Experimental data are presented on the transient behaviour of an industrial scale shell-and-tube exchanger condensing a mixture of steam and air under reduced pressure. The system was subjected to step changes in the five key loads which determine the condenser behaviour. These are the inlet pressure, steam flowrate, air flowrate, coolant flowrate and coolant inlet temperature. The experimental equipment and its associated instrumentation are described. The experiments performed are detailed and the results from two representative runs are presented and discussed. An understanding of the process is a necessary pre-cursor to modelling and simulation.