Reports that the U.S. Department of Energy in collaboration with industry is developing a tool that automates detection and diagnosis of problems associated with outdoor air ventilation and economiser operation. States that the tool, known as the outdoor air/economiser(OAE)diagnostician, monitors the performance of air handling units (AHUs) and detects problems with outside air control and economiser operation, using sensors that are commonly installed for control purposes. The OAE diagnostician is currently installed and operating on AHUs in two buildings. Presents and discusses the positive test results. Concludes by noting further possible applications to building systems and equipment for automated diagnostics.