August in St. Louis means the AC has been running hard for months, and it’ll keep running hard through September. If you’ve been thinking about scheduling a tune-up but wondering whether it’s too late in the season to bother, the short answer is no. The second heat stretch of a Missouri summer is exactly when a tired system is most likely to fail. It’s also most likely to cost more to run than it should. We’ve been servicing AC systems in St. Louis since 1964, and mid-season tune-ups consistently turn up the same issues that cost homeowners real money when left unaddressed.
The visit itself is straightforward. A professional tune-up covers inspection, cleaning, and a performance test. Nothing needs to be broken before you schedule one. Here’s what happens from the time our technician arrives to the moment they walk you through their findings.
What an AC Tune-Up Actually Is (and Is Not)
A tune-up is preventive maintenance, not a repair call. The distinction matters because a lot of homeowners hold off on scheduling until something stops working. By that point, what might have been a $15 capacitor replacement has become an emergency compressor call on a 95-degree afternoon. Every professional tune-up follows a three-phase structure: inspection and testing of indoor and outdoor components, cleaning of coils and the condensate drain line, and a performance test under real operating conditions. St. Louis typically sustains high heat and humidity well into September, so a tune-up done in August still protects your system through the rest of peak cooling season, not just the next one.
What the Technician Checks: The Indoor Unit
The indoor portion of the visit covers the components that move and condition air through your home.
- Air Filter
The technician inspects the filter and replaces it if needed. A clogged filter forces the blower motor to work harder than it should, and it’s the single most common cause of reduced airflow and climbing energy bills. If your filter hasn’t been changed in a few months, this one step can make an immediate difference in how the system runs. - Evaporator Coil
The evaporator coil sits inside the air handler and absorbs heat from the air passing over it. Dust buildup on the coil slows that heat transfer, which means longer run times and uneven cooling from room to room. The technician cleans the coil surface to restore proper contact between the refrigerant and the air stream. - Condensate Drain Line
As your AC cools air, it pulls moisture out of it. That moisture collects in a drain pan and exits through the condensate drain line. In St. Louis’s humidity, algae and debris build up in that line faster than in drier climates. A clogged drain causes water to back up into the pan, which triggers the safety float switch and shuts the system off. Sometimes this happens without any other warning. Our technicians clear the line and check the pan for standing water or staining that might indicate a recurring problem.
What the Technician Checks: The Outdoor Unit
The outdoor condenser unit takes the heat pulled from your home and releases it outside. When it can’t do that efficiently, everything downstream gets harder.
- Condenser Coil
Over a cooling season, the outdoor unit collects leaves, grass clippings, cottonwood, and general debris. That material blocks airflow through the condenser coil and traps heat inside the unit, raising compressor strain and shortening the component’s lifespan. The technician cleans the coil fins and checks the surrounding area for airflow restrictions. - Refrigerant Charge
Refrigerant is measured against the manufacturer’s pressure specifications for your specific system. Low refrigerant doesn’t happen from normal use. It means there’s a leak somewhere. Adding refrigerant without finding the source is a temporary fix at best. Our technicians identify low charge, trace the cause, and explain what a repair would involve before anything is added. - Capacitor, Contactor & Electrical Connections
The capacitor helps start and run the compressor and fan motors. The contactor is the electrical switch that tells those components to turn on. Both wear down over time, and both are among the most common failure points in systems more than a few years old. Loose wiring connections create resistance and heat. The technician tests these components for proper function and checks connections throughout the unit.
The Performance Test & What You Hear at the End
Once cleaning and inspection are complete, the technician runs the system and measures the temperature split between the return air coming in and the supply air going out. A well-functioning system typically produces a differential of 14 to 22 degrees Fahrenheit. A number outside that range points to airflow problems, refrigerant issues, or coil performance concerns worth investigating further.
After the test, you get a plain walkthrough of what the technician found, what was corrected during the visit, and what, if anything, should be monitored or addressed before next season. Our NATE-certified technicians diagnose from measurements and observations, not from a script. If everything checks out, we tell you that. If something warrants attention, we explain what it is and why it matters before recommending anything.
How a Tune-Up Protects Your Investment Beyond This Summer
The most immediate payoff is a system that runs efficiently through the rest of cooling season. A clean, properly charged AC uses less electricity per hour of operation, and across a Missouri summer with sustained high cooling loads, that can add up on your utility bill.
There’s also a warranty consideration most homeowners don’t think about until it’s too late. Many HVAC manufacturers require documented annual professional maintenance as a condition of their parts warranty. Skipping a year doesn’t just leave the system unserviced. It can void coverage on a compressor or coil replacement that would otherwise be covered. Keeping a maintenance record protects that investment.
A tune-up finding that needs follow-up work doesn’t have to wait. Martin-Jetco Heating and Air Conditioning offers same-day service, so if the inspection turns up something that warrants attention, we can address it quickly. To schedule an AC tune-up in the St. Louis area, give us a call at (636) 205-1631 or message us online.