This paper analyzes a renewal input working vacations queue with change over times and Bernoulli schedule vacation interruption under (a,c,b) policy. The service and vacation times are exponentially distributed. The server begins service if there are at least c units in the queue and the service takes place in batches with a minimum of size a and a maximum of size b (a<=c <= b). The change over periods follow if there are (c-1) customers (at vacation completion instant) or (a-1) customers at service completion instants. The steady state queue length distributions at arbitrary and pre-arrival epochs are obtained. Performance measures and optimal cost policy are presented with numerical experiences. The genetic algorithm and quadratic fit search method are employed to search the optimal values of some important parameters of the system.