1. A diagnostic apparatus for examining a heating, ventilation, and air conditioning (HVAC) system, said apparatus comprising: a control unit detachably connected to the HVAC system, said control unit controlling a plurality of control parameters of the HVAC system; and means for said control unit to monitor a plurality of performance characteristics of the HVAC system; whereby said control unit monitors the plurality of performance characteristics while controlling the HVAC system to provide a diagnostic check of the HVAC system.