We purchased a house in the winter and now that summer has rolled around it is too hot. The ac is set to 70-72. The return air is 85. Temp at registers is 66. Outside temp is 95. I know the 19 degree between the register and return is great but why isn't my house cooling down? Ac is running 24/7 because it can't lower the temp.

It could be many things. The unit is not large enough for the house. It is low on freon (or what ever it uses). Have you had anyone out to look at it?

Is it a central unit ? What size is it ? How big is house ?

We have a central Unit. It's a Lennox gcs16r-411-100-5p and it's a 3 ton unit. The house is ~1500 sqft of cooled space. We're having someone come out later this week I just wanted to see if this was a common issue or if something doesn't seem right since it our first house.

No, it's not unusual to find stuff that needs attention in a house you just moved into. Its more normal than NOT because a house requires regular maintenance. It can be frustrating and expensive and that too is pretty normal, but you get use to it, and learn as you go.

A good handyman/contractor you trust is worth his weight in gold.

Read up on some of the stuff people go through on THIS forum.

Most summer problems with "not cool enough" have to do with solar load and not enough insulation or venting in the attic. The real clue is when it will shut off at night but runs all day. Look at your ambient temp. 70-72* is not reasonable with 95* if you have full solar load, particularly if the supply ducting is in the attic.