The air is blowing, but it's not cold
You've probably noticed the vents are still pushing air, maybe even a decent amount of it, but the house isn't cooling down the way it should. Someone in the family says the thermostat fan switch, set to 'on' instead of 'auto', is the reason the house feels warmer. That's a reasonable guess, and it's worth checking before you assume the compressor is dying. But in a lot of Nixa homes this time of year, the fan setting is a symptom people notice, not the actual cause.
What the fan switch actually does
'Auto' means the blower only runs when the system is actively heating or cooling. 'On' keeps the blower running continuously, whether or not the compressor outside is cycling. When you leave it on 'on' through a humid Ozarks summer, the blower keeps moving air across the evaporator coil even after that coil has warmed back up between cooling cycles. That air picks up some of the moisture the coil had just pulled out of it and carries it right back into the house. The result is air that's technically moving but feels warmer and stickier than it should, especially in the afternoons when Nixa's humidity sits heavy.
If your house has felt muggier than usual despite the AC running, check that switch first. Flip it to auto and give it a day. In older homes around town, especially ones built in the 70s and 80s with single-stage systems, this one setting can make a noticeable difference in comfort without touching anything mechanical.
More on this from The Fan Setting That Makes The Air Feel Warmer.
Why this matters more with Nixa's housing stock
A lot of homes in and around Nixa, especially in the older neighborhoods near downtown and out toward Spur Drive, were built before continuous-run blowers and variable-speed systems were common. These houses often have single-stage AC units paired with simple thermostats, which means the fan setting carries more weight than it would in a newer build with a smart multi-stage system designed to manage humidity on its own.
Add in that most Nixa attics run hot and underinsulated by modern standards, and ductwork running through those attics loses some of its cooling before it ever reaches a vent. If the blower is running constantly on an 'on' setting, it's pulling warm attic air through ducts more often too, which compounds the problem instead of fixing it.
What else to check before you call someone
Once you've confirmed the fan is set to auto, walk through a few other things yourself. Check that your filter isn't clogged, since restricted airflow makes a system labor harder and blow warmer air regardless of fan setting. Look at your outdoor unit and clear away any leaves, grass clippings, or mulch that's built up against the coils, common this time of year when yards get mowed often. Confirm your supply vents aren't blocked by furniture or rugs, which is an easy thing to overlook in a house that's had furniture rearranged recently.
If you've done all that and the air coming from the vents still feels warm rather than cold, not just humid, that's a different problem than a fan setting. That usually points to low refrigerant, a failing compressor, or an issue with the outdoor unit itself.
When it stops being a DIY fix
If adjusting the fan setting and cleaning up the obvious stuff doesn't change anything within a day or two, you're past the point where a homeowner can reasonably diagnose further. Refrigerant leaks need to be found and sealed by someone with the right gauges and license, not guessed at. A compressor that's short-cycling or struggling under Nixa's July and August heat can get worse quickly if it's ignored, and running a failing system hard in that heat tends to turn a repair into a replacement.
The practical rule is this: if the air is cool but the house still feels damp, check your settings and filters first. If the air itself isn't cold anymore, or the outdoor unit is making noises it didn't used to make, that's a call for a technician who can get a gauge on the system rather than another day of waiting to see if it resolves on its own.