I am trying to figure out if I have a problem, or if this is just normal.. I live in SQ Missouri, the outdoor temp right now is 90. My home is not very large, maybe 1250 sq ft with 3 BR. We have been miserable this summer with regards to indoor temp control. We have all windows shut and blinds closed, doors shut, garage door shut, etc. No traffic coming in or out so not opening and closing exterior doors. Our AC unit cannot keep up at all. We have it set at 74, and for a few hours in the morning it can maintain that temp, but once the outside temp starts creeping above 85 or so (around noonish), the AC can no longer keep up. Last night, around 8PM, it was 82 inside our house, and the AC has been running non-stop all day long.

One other thing I have found, the furnace/blower is located on one side of the house. The closest vent to the furnace registers ~60 at the opening, and has a very strong airflow. Now, when I got to the opposite end of the house in our Master BR (and where the internal thermostat happens to be located), the vents are registering ~65 at the opening, and have a significantly noticeable reduced airflow by comparison. I would expect the vents closer to the source to have higher flow, but should it be that noticeable? Also, is a 5 degree loss from one side to the other normal? I am guessing if the vents all blew at 60 it would be much more capable of holding the overall temperature.

Should a properly sized/functioning system be able to maintain 74 inside when outdoor temps are 90-95, or is -20 differential asking too much?

Also, even when it's not blistering hot outside, our unit pretty much runs non-stop, unless we shut it off. Our neighbor 4 houses down runs her thermo at about 75-76 all day, has no trouble maintaining that temp, and says her unit is off/on rather than running continuously. Her electric bills are also about half ours, even though her house is around 400-500 sq ft. larger.

Thoughts?