A monitoring system for monitoring operation of a refrigerant-cycle system is disclosed. A condenser unit sensor measures an operating characteristic of a condenser unit, the condenser unit including a condenser and a compressor. An evaporator unit sensor measures an operating characteristic of an evaporator unit, the evaporator unit including an evaporator and a fan. An electrical sensor measures an electrical quantity indicative of power consumption of the refrigerant-cycle system. A processing system calculates an efficiency of the refrigerant-cycle system based on the power consumption of the refrigerant-cycle system, the operating characteristic of the condenser unit, and the operating characteristic of the evaporator unit.