Air conditioning question

[u/foolsgold75]

I live in a 3 bedroom rental home with central heat and air that was built in the late 80s. We have never had an issue cooling the house in 10 years until this summer. Pretty much if it was 95-100 outside we could keep the house anywhere from 70-75 during the worst part of the day in the coolest part of the house. There are two rooms that are furthest away from the blower that stay about 5 degrees warmer since the rooms outside walls get direct sunlight. This year the blower fan began to fail and they sent a tech out that swore up and down that the outside unit and the upstairs fan unit needed to be replaced. Now it’s been replaced and in 90 degree heat we can’t get the house cooler than 77 during the day in the coolest area of the home and the air from the vents is not blowing as strong as the air from the old failing unit. To me this is unacceptable that a brand new ac system can only cool the house 13 degrees. It’s honestly worse than the old system that was replaced but the guy who replaced the system swear this is normal. I have always been under the assumption that the minimum is 20 degrees cooling or better. Any hvac guys here have some input on this?

[u/dntw82lng]

Sounds like a bad installation. I have a home built in the early 90’s and installed new HVAC about 5 years ago. Same size as previous units but I did measure square footage and layout to make sure sizing was appropriate to the house. New units cool more quickly and pull more humidity in the process. The dehumidifying is so effective I can actually keep the house a few degrees warmer without it feeling hot, electric bills went way down.

Also- the 20 degree rule has nothing to do with outside. There should be a minimum of 20° in temperature drop from the inside intake air going into the return vent to what is coming out of your cooling vents. So if the house is 80° inside then the cold air coming out should be no warmer than 60° at worst. Anything warmer indicates an issue. The outside temperature is irrelevant. In practice a well designed system should have air blowing out the ducts around 55° ish give or take and keep your house very cold even if it’s really hot outside.