Measured EER and COP are affected by the load under which an air conditioning, refrigeration or heating system is running; the load is a function of the evaporating and condensing temperatures. The invention makes adjustments for the purpose of maximizing measured EER and COP in a feedback loop utilized to optimize cooling or heating capacity relative to power consumed. The maximum EER is continuously achieved by incrementally adjusting each operating parameter to realize an incremental increase in EER, even as conditions such as ambient temperature are changing.