The efficiency of air conditioners is often rated by the Seasonal Energy Efficiency Ratio (SEER). which is defined by the Air Conditioning, Heating, and Refrigeration Institute in its 2008 standard AHRI 210/240.
The SEER rating of a unit is the cooling output during a typical cooling-season divided by the total electric energy input during the same period. The higher the unit’s SEER rating the more energy efficient it is. In the U.S., it is the ratio of cooling in British thermal unit (BTU) to the energy consumed in watt-hours.
AHRI Certification Directory
Whether you’re a consumer or a contractor, use this site to search for the efficiency rating of an HVAC system. The site will look like the picture below. You will need to know the type of your AC system (Heat Pump, Air Conditioner, Boiler, Furnace, etc.), and have model numbers of indoor unit and outdoor unit on hand.
Screengrab of the AHRI website
Example of an AHRI certificate