Two-Stage Units run at two different speeds; low and high speed. 80% of the time your desired indoor temperature is reached at low speed, but when it is not possible, the compressor runs at high speed.
The following video shows an example of how two-stage units operate. We will also give you some example about when is better to choose a two-stage unit over a single-stage or variable speed units.
You can also review the following videos for more information: