How to tell if e air blowing out fr our house's air-condition unit is still good n fresh?

Well if you don't have a stinky house ie: pet orders, cooking orders, sewer drains etc. and it smells fresh in your house when the A/C isn't running then when it is running it will be fresh too. All an A/C is a dehumidifier which removes the humidity from the conditioned space. Which makes the air cool. The air coming out of your vents is the same air that's in your house, it just circulates the air