Your home is kept cool by moving heat energy out of it, not by blowing cold air into it. Look outside at the air conditioner: There isn’t any ducting running from the unit inside your home. That’s because an air conditioner’s job is to compress a gas called refrigerant.
When compressed, the gas condenses down to a chilled liquid. The air conditioner pumps this inside to the indoor coil. Warm air from the home is forced through the coil (by the fan motor in the furnace), and the refrigerant absorbs heat energy from the air.
The efficiency of an air conditioner is measured with a SEER rating. But here’s something to know: this rating is determined by the air conditioner’s efficiency at full capacity (full load). But most of the time, an air conditioner doesn’t need to run at full load. An air conditioner with a two-stage or variable stage compressor will save you a lot of money over a single stage unit. If comparing models, and you see two that are the same SEER, but different in price, check the details on the compressor.