Predictive maintenance method and apparatus for use with heating, ventilation, air-conditioning and/or refrigeration (HVACR) systems are disclosed. The preferred apparatus includes a dozen temperature sensors strategically located within and HVACR system to sense various operating temperatures and three electrical current sensors to sense various operating electrical currents. HVACR system conditions are measured periodically by an on-site service technician and inputted to a computer that identifies and reports the potential trouble spots represented by out-of-range measurements. The computer is programmed to produce graphs, tables and prediction commentary.