This paper presents an automatic commissioning tool based on a FDD (fault detection and diagnosis) strategy for typical VAV (variable air volume) air distribution systems. The framework of the FDD strategy is established based on system knowledge, qualitative states and object-oriented SPC (statistical process control) models. Eight FDD schemes are set up to detect the eleven VAV root faults within the qualitative/quantitative FDD framework to form the FDD strategy consisting of two steps. Ten faults, which would affect the system operation, are detected at the first step. The eleventh fault, which would not affect the basic system operation but would lead to imperfection under advanced supervisory control, is detected at the second step. The FDD strategy is tested and validated on typical VAV air-conditioning systems involving multiple faults both in simulation and in-situ tests. A software package is developed as a BMS-assisted automatic commissioning tool. ; Department of Building Services Engineering