An apparatus includes a voltage sensor, a current sensor, and a controller. The voltage sensor measures voltage values of alternating current power supplied to a capacitor. The capacitor is electrically coupled to a compressor. The current sensor measures current values of the alternating current power. The controller is configured to receive the voltage values and the current values. The controller is configured to determine a first power factor value based on at least one of the voltage values and at least one of the current values. The controller is configured to selectively detect a first capacitor fault in response to concurrent determination that (i) the first power factor value is less than a first power factor threshold and (ii) a first current value of the current values is greater than a first current threshold. The first capacitor fault indicates that a capacitance of the capacitor has degraded.