Q.Boston Fern
The tips of the fronds of my fern are turning brown and shriveling. It is indoors in diffused light. I think it is being properly watered. It is near a vent where it gets air conditioning. Could this be the problem?

The location near an air conditioning unit is likely some cause of your issues.
I would move to a location that would meet the ferns needs.
Here are links for you with more information.
https://www.gardeningknowhow.com/houseplants/boston-fern/boston-fern-care.htm
https://www.gardeningknowhow.com/houseplants/boston-fern/boston-fern-misting-needs.htm
https://www.gardeningknowhow.com/houseplants/boston-fern/watering-boston-ferns.htm