Systems and methods for determining the health of a compressor are disclosed. In one embodiment, a prognostic-diagnostic unit (PDU) compares expected compressor power consumption, based on current operating conditions of the HVAC system, to actual compressor power consumption. If the actual power consumption is within a predefined range of the expected power consumption under current operational conditions, the HVAC system is determined to be operating properly. If the actual power consumption deviates from the expected power consumption, a fault is indicated. An appropriate action is taken, such as displaying a fault alert, transmitting a fault message to another device, and storing information relating to the fault for later retrieval to assist troubleshooting.