An HVAC controller, a method of operating an HVAC controller and an HVAC system employing the controller or the method. In one embodiment, the HVAC controller includes: (1) a processor couplable to at least two refrigerant pressure sensors via separate data paths to receive input signals therefrom and further couplable to a compressor stage and a condenser fan to provide output signals thereto, and (2) memory coupled to the processor and storing a software program having program instructions capable of causing the processor to command the compressor stage or the condenser fan to turn on irrespective of a state of an input signal generated by either of the at least two refrigerant pressure sensors, and generate an error message at least partially depending upon whether or not a high pressure shutdown occurs after the processor commands the compressor stage or the fan to turn on.