An HVAC system includes a reversing valve configured to receive refrigerant and direct the received refrigerant based on an operating mode of the HVAC system. The HVAC system includes first and second sensors. A sensor measures a heat-exchanger temperature associated with the outdoor heat exchanger. A controller monitors an outdoor temperature and the heat-exchanger temperature and compares these temperatures. The controller determines whether the HVAC system is intended to operate in a cooling or heating mode. If the heat-exchanger temperature is less than the outdoor temperature and the HVAC system is intended to operate in the cooling mode, the controller determines that a first reversing-valve fault is detected. The first reversing-valve fault is associated with the reversing valve being in the heating configuration when the HVAC system is intended to operate in the cooling mode.