The new unit still isn't fixing the problem
You replaced the air conditioner, maybe because the old one was fifteen years old and couldn't keep up, and you expected the house to finally feel even. Instead the upstairs bedrooms in your north Springfield two-story are still warm at ten at night in July, while the living room near the thermostat feels fine. The new equipment runs more quietly, cycles differently, maybe even uses less electricity. But the hot spots are still hot. That's usually not a sign the new unit is defective. It's a sign the ductwork it's pushing air through was sized for a smaller or older system, and it was never upgraded when the new one went in.
Why Springfield homes run into this so often
A lot of housing stock in this part of southwest Missouri, especially in neighborhoods north of downtown and out toward Republic Road, dates from the 1960s through the 1980s. Those homes were built with ductwork sized for the cooling loads and equipment common at the time: smaller tonnage units, less insulation, different expectations about how hard an AC would need to work. Ozarks summers bring stretches of high heat and heavy humidity, July and August especially, and the duct system has to move a lot of conditioned air quickly to keep a house comfortable through that. If the trunk lines and branch runs were never resized, a bigger or higher-efficiency replacement unit is trying to force more air through a passage that can't carry it.
More on this from Why A Retrofit Duct System Caps What A New Air Conditioner Can Deliver.
What a capped duct system actually looks like day to day
The symptoms are usually subtle at first. Some rooms cool fine, others lag behind by several degrees no matter how long the system runs. The system seems to run constantly during the hottest part of the afternoon without ever quite catching up. You might notice a whistling or rushing sound at certain supply vents, which is air being forced through an opening too small for the volume trying to pass. Your energy bills may be higher than the new unit's efficiency rating would suggest, because the system is working harder and longer to compensate for restricted airflow. None of these are dramatic failures. They're a system quietly running below its potential, month after month.
What you can check yourself
Start by walking the house with your hand near each supply vent when the system is running. Weak or barely-there airflow in certain rooms, compared to strong flow elsewhere, points toward a duct sizing or balance issue rather than a thermostat problem. Check return air grilles too. Older Springfield homes often have just one or two returns for an entire floor, which was fine for the equipment of that era but can starve a larger modern system of the air it needs to pull back in. Look in your attic or crawlspace, if you can access it safely, for ductwork that looks pinched, crushed, or disconnected at the joints. You can also just track which rooms are consistently uncomfortable and note the time of day, since that pattern is useful information to hand to a technician rather than something you need to diagnose on your own.
Where this stops being a DIY job
Sealing an obviously disconnected duct joint with mastic tape is reasonable homeowner work. Deciding whether your trunk line needs to go from eight inches to ten, or whether you need a second return added on the second floor, is not. That requires a load calculation and airflow measurement, the kind of static pressure testing that tells a technician whether the blower is fighting the ductwork or working with it. This is where you want someone doing hvac services north springfield to actually test the system rather than guess. A correctly sized new air conditioner paired with undersized ductwork will never perform to its rating, no matter how good the equipment is, and no amount of thermostat adjusting fixes a physical bottleneck in the duct run.
What to ask before you replace anything else
If you're facing another equipment replacement down the road, ask whether a duct evaluation is part of the process, not an afterthought bolted on after the new unit is already installed. In a city like Springfield, where summer humidity makes even a well-sized system work hard, matching the ductwork to the equipment matters as much as the equipment itself. A new, efficient air conditioner connected to the same undersized, decades-old ductwork will disappoint you in exactly the same way the old one did, just with a lower utility bill while it does it.