Abstract: A system and a method for detecting and diagnosing faults in heating, ventilating and air conditioning (HVAC) equipment is described. The system comprises a sensor; a classifier modelling a normal behaviour of the HVAC equipment in situ in the installed operation environment, the classifier having a plurality of classifier parameters for computing a classifier score using an input data based on a measured value from the sensor, the plurality of classifier parameters being created during a training phase of the system using the input data during the training phase; and a decision module for comparing the classifier score to a decision threshold, the decision threshold being set during the training phase.