I have a new home and new a/c, and a urine smell comes out of the vents after it reaches the set temp. How can I get a fresher smell out of it?

Spray Fabreeze into the return duct while the blower is running. The sub contractors that built your home probably used the duct as the toilet.

I have a new home and new a/c, and a urine smell comes out of the vents after it reaches the set temp. How can I get a fresher smell out of it?
You could call a duct cleaning specialist who would come out, scrape and vacuum the ductwork and then sanitize the entire system. This would probably cost a couple hundred dollars but would be worth it to know the ductwork is clean and bacteria free.

What has probably happened is either your cat peed in the vent or one of the construction workers did. Cleaning and/or sealing the vent where the odor is coming from will not help the problem. If you are handy and can get to the heat pipe (in the basement) you should pull the pipe down and spray it inside with OdorXit Concentrate diluted in water. OdorXit.com, otherwise you will have to try to spray the inside of the pipe with OdorXit and hope you can reach the problem area. Good luck!

I have a new home and new a/c, and a urine smell comes out of the vents after it reaches the set temp. How can I get a fresher smell out of it?
You can spray ep[leon nnz in to the vents .it is available on line. Knocks out the smell.

Are any of your supply or return vents in the floor? If not it is not the cat or dog. Nature's Miracle will actually consume (eat) the urine if you can find its location.