Why the air feels weaker than it should
You turn the thermostat down another two degrees because the house still feels sticky. The vents are blowing, but what comes out feels more like room temperature than cold. So you bump it down again, maybe switch the fan to 'on' instead of 'auto,' figuring more air movement will fix it. In a lot of homes around Nixa this time of year, that's the exact move that turns a minor problem into a dead system by evening.
What's happening inside the unit is simple, even if it's hidden behind a cabinet or tucked outside under a maple tree. The indoor coil, the part that actually pulls heat and humidity out of your air, has started icing over. Once ice forms, it blocks airflow across the coil. Less airflow means the coil gets colder still, which means more ice. It's a loop, and every cause has it feeding on itself.
What Nixa's climate does to push things that way
Southwest Missouri summers aren't just hot, they're wet. The humidity that rolls up from the Ozarks and sits over Christian County puts a heavier moisture load on your AC than a dry-climate system ever has to handle. Your coil is working overtime pulling water out of the air, not just cooling it, and that extra duty makes it more sensitive to anything that restricts airflow.
A lot of the housing stock here, the ranch homes off Tracker Road, the older places near downtown, the newer builds out toward Christian County, still rely on ductwork that was sized decades ago or added onto piecemeal as additions got built. Undersized returns, a few crushed flex ducts in a crawlspace, a filter nobody's changed since spring. Any one of those cuts down airflow just enough that on a 95 degree, soup-thick July afternoon, the coil tips over into icing.
More on this from Reading List The Ice Loop And Why Running It Harder Makes It Worse.
Why turning it up harder backfires
The instinct to crank the thermostat lower or run the fan constantly makes sense. The house is warm, you want it cooler, you assume the machine just needs to work harder. But if the problem is restricted airflow, asking the compressor to run longer and colder does not clear the blockage. It accelerates the ice buildup.
Once a decent layer of ice forms on the coil, the system can go from 'not cooling well' to 'not cooling at all' in a matter of hours. Worse, if you keep running it in that state, liquid refrigerant can make it back to the compressor instead of fully evaporating first, which is one of the more expensive ways to damage a system. The fix for an icing coil is never 'more cold.' It's figuring out what's choking the airflow.
What you can actually check yourself
Start with the filter. In this region, with cottonwood fluff in early summer and cut grass dust all season, a one-inch filter can load up fast, sometimes faster than the three-month schedule printed on the box suggests. Pull it and hold it up to a light. If you can't see light through it, replace it.
Walk around and check that supply vents and return grilles aren't blocked by furniture, rugs, or boxes, which is common in finished basements and additions. If you have a crawlspace, a quick look for disconnected or crushed flex duct is worth doing, especially after any work done under the house.
If you already see frost or ice on the indoor unit, on the line set, or dripping water where there shouldn't be any, turn the system off entirely and switch the fan to 'on' so it can thaw, which usually takes a few hours. Don't run the compressor again until it's completely clear.
Where this stops being a DIY job
If the ice keeps coming back even after a fresh filter and clear vents, the cause is usually something you can't see or fix from inside the house: low refrigerant charge, a failing blower motor, a dirty coil that needs a real cleaning, or ductwork that's undersized for the house's square footage. Low refrigerant in particular causes icing and isn't something to top off yourself, since a system low on charge usually has a leak that needs finding first.
This is also where repeated icing starts costing real money if it's ignored. Compressors don't recover well from repeated liquid slugging, and a coil that's iced over and thawed a dozen times a summer wears out faster than one that's never had the problem. If the loop keeps restarting after you've done the simple checks, it's time to get someone out to look at refrigerant levels, duct static pressure, and the coil itself before the next heat wave finishes the job.