So called “Central” Air conditioners (AC) which are units that sit outside and use air vents throughout your house work by pulling air from the inside of your house and sending it into your furnace (hopefully through the air filter that sits next to your furnace (Change this filter often)).
Above your furnace sits a object known as the A-coil. This is basically a radiator similar to what is toward the front of most car engine spaces. The entire job of the outside AC unit is to make this (A-coil) radiator very cold. As the furnace sends the air through the A-coil it becomes very cold, from that point it travels through your duct work and comes back to the living spaces as cold air through the air vents.
When air becomes colder it can hold less water so water condenses on the A-coil and drains out of the furnace. Most air pollutants like dust get trapped by the air filter before making it to the furnace (which is why you need to change it so often) Other than what gets trapped in the air filter most of the rest of this just stays in the air and comes right back out.
Edit: Typos and bonus fact: The radiator bit is called an A-coil because it’s shaped like an A
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