Fault detection and diagnostics applied to heating, ventilating, and air-conditioning (HVAC) equipment has been an active area of research over the past decade, with much of the work focusing on air distribution systems. Concurrent efforts have sought to improve the control of these systems. This paper discusses the relationship between controls and diagnostics for air distribution systems, provides an overview of the diagnostic literature for these systems, presents new findings from a diagnostic method that enables operational characteristics of individual HVAC components to be extracted from high frequency measurements of whole-building power and outlines research challenges that remain to be addressed.