A method of monitoring performance of an electric motor includes calculating an actual input power and an expected input power of the electric motor. A power difference between the actual input power and the expected input power is recursively calculated over at least one period of an electrical cycle of the electric motor to determine a variance in the power difference during the at least one period of the electrical cycle. The variance in the power difference is compared to a threshold value to determine if the variance in the power difference is greater than the threshold value or less than the threshold value. The control module may signal that the electric motor is not operating within allowable operating parameters when the variance in the power difference is less than the threshold value.