A method is provided and may include generating a high-side signal indicative of an operating condition of a high-pressure side of a refrigeration circuit and generating a low-side signal indicative of an operating condition of a low-pressure side of the refrigeration circuit. The method may further include processing by a processor the high-side signal and the low-side signal to determine a non-measured system condition and determining by the processor an efficiency of the refrigeration circuit based on the non-measured system condition.