An air conditioner is a single unit that cools the air in a room or building. It works by drawing in hot air from the outside, cooling it, and then circulating it back into the room. A HVAC (Heating, Ventilation, and Air Conditioning) unit is a system that combines both heating and cooling capabilities. It works by drawing in air from the outside, heating or cooling it, and then circulating it back into the room. HVAC systems are more efficient than air conditioners because they can both heat and cool the air, allowing for more precise temperature control. Additionally, HVAC systems are more energy efficient than air conditioners because they can be programmed to run at different times of the day, allowing for more efficient use of energy.