A single-stage air conditioner has been around for while, it was the only technology available in the market for a long time. What it means is that, your air conditioning unit will work full power until it reaches the temperature desired set on the thermostat. Once the temperature set has been reached it will turn off and only turn on again as the room gets warmer and needs to be brought back to the temperature on the thermostat. There is no other setting, or intermediate, it’s either running in full power or off. This causes a high electricity bill due to the spikes of power required to run full power. It’s like when you are driving and steps on the gas pedal all the way, completely stops and continues in that driving mode. It will take a lot more gas as if you were to drive at a constant speed. Single stage equipment usually costs less money up front, but over time it will end up costing more because of operating and maintenance expenses.