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Technician Checking Air Conditioner

What is a Two-Stage Cooling System?

The compressor is the standout feature of a two-stage, air-conditioning system that differentiates it from a standard, single-stage cooling system.

Standard systems run at one speed only: high. When you need to cool your home, the A/C cycles on at full blast, whether you need that much conditioned air or not. Often, this equates to a significant amount of wasted energy and fewer dollars in your pocket.

Two-stage cooling systems employ a compressor that runs at two speeds: low and high. In addition, these advanced systems generally also use a variable-speed air handler to simultaneously adjust the amount of air that moves into the home, providing the ultimate experience in comfort and efficiency.

Side View of Amana Air Conditioner

Meeting the Cooling Demands

A two-stage cooling system runs at its lower speed about 80 percent of the time. This speed is sufficient to meet the cooling load of your home during warmer spring days or mild summer days, as well as cooler mornings and evenings. However, even as temperatures ramp up, running at the lower speed is often enough to generate comfort.

A two-stage cooling system operating at the lower speed of operation, which hovers around 67 percent as opposed to 100 percent runs nearly continuously. Continuous operation means that the air conditioner hardly shuts on and off. By avoiding the constant on-off cycle, the two-stage cooling system delivers significant advantages, such as better dehumidification, longer life cycle and lower energy costs.

With the ability to ramp up its cooling capacity, the two-stage cooling system adjusts precisely to the home's load when temperatures become extreme. When relative humidity soars and temperatures rise, the two-stage compressor responds, immediately adjusting its output to the higher speed to keep up with demand.


While improved energy costs may be enough to convince homeowners of its benefits, the two-stage cooling system delivers additional perks, like these:

Improved humidity control. When the A/C runs continuously, it can dehumidify the air better. Short but strong blasts of air don't provide enough time for the A/C to remove water vapor from the air inside your home, but a continuous operation gives the coils sufficient time to draw water vapor into the system and evaporate.

Comfort. The on-off cycling often leads to drastically differing temperatures in the home, depending on whether the system is running or off. Typically, when the A/C starts up, it delivers a strong blast of chilly air, often making home occupants very cold. But as soon as the system shuts down, and there's no air movement in the home, the home quickly becomes hot and stuffy. Operating in continuous mode helps the two-stage system bypass this problem, circulating just enough air in the home to make it comfortable, with little variation in temperature.

Longer service life. A compressor that shuts on and off a lot is subject to increased wear and tear, and will eventually wear out and then break down. With less on-off cycling, the two-stage compressor lasts longer, especially if you schedule annual preventive maintenance for your cooling system.

Improved Winter Comfort. As a result of using the variable speed indoor unit, you get the ability to "throttle" heat delivery. Lower heat output at a slower speed increases comfort, saves fuel and doesn't over dry the indoor air. Full heat output is delivered as needed based on thermostat demand and user settings.

With so much at stake when it comes to home cooling, take the time to consider your options when you're facing an air conditioner replacement. Two-stage systems cost more initially but deliver significant perks on the back end for homeowners who invest in them.