Why Air Conditioners Fail in Late August (and What to Do When Yours Does)

Ask anybody in this trade which weeks of the year the phone rings hardest, and you'll get the same answer: the last two weeks of August and the first hot week of September.

Not June. June has its own rush, when everyone turns the system on for the first time and finds out it didn't survive the winter. But the late-August calls are different. These are systems that ran fine all summer. They cooled the house through the Fourth of July and through the heat wave in the middle of the month, and then one sticky afternoon with the thermostat reading 78 and climbing, they just stop.

There's a reason for that, and once you know it you'll have a better idea what to check, what to expect, and whether it's even worth fixing this late in the season.

Why the Calendar Matters

An air conditioner has parts that wear a little with every start and every hour of run time. By late August, your system has been starting and stopping several times an hour, nearly every day, for close to three months. Whatever margin those parts had in June is mostly gone.

Then the weather piles on. Late August in West Michigan is when we get the humid stretches, the days where the temperature says 88 but the air off the lake makes it feel like 95, and the nights don't cool off enough to give the equipment a break. The system runs long cycles with the least margin it's had all season. It's the same reason a worn tire fails on the highway and not in the driveway.

Two other things stack up in the background. Condenser coils have been collecting cottonwood, grass clippings, and dust since May, and a coil that was 80 percent clear in June might be half-blocked now. And filters that got changed in the spring, when everyone was thinking about it, are usually overdue by August.

The Parts That Actually Fail

Most late-summer no-cool calls come down to a handful of causes, and a couple of them you can spot yourself.

The capacitor. This is the number one late-summer failure by a wide margin. The capacitor stores an electrical charge and gives the compressor and fan motor the kick they need to start. It's a small can that lives inside the outdoor unit, and heat is what wears it out. A capacitor that's been baking in a metal box all summer loses strength gradually, then quits. The symptom is an outdoor unit that hums but doesn't start, or a fan that sits still while the compressor tries, or a system that starts hard and then trips. It's an inexpensive part and a fast repair, and it's the repair I'm happiest to make because the customer's afternoon started with "I think we need a new air conditioner."

The contactor. This is the switch that connects power to the compressor when the thermostat calls. The contacts arc a little every time they close, and after a few thousand cycles the surface gets pitted and burnt. Eventually it welds shut (the unit runs constantly and won't stop) or fails open (the unit does nothing). Another modest part, another quick fix, another one that heat and run time accelerate.

A dirty condenser coil. The outdoor unit's whole job is dumping heat out of your house into the yard. It can't do that through a mat of fluff. A blocked coil drives pressures and temperatures up until the compressor's internal overload trips to protect it. Then it cools off, restarts, overheats, trips again. If your unit runs a while and then goes quiet with the fan still spinning, walk out and look at the fins. Cleaning the condenser is a job most people can do with the power off and a garden hose, and it solves more August calls than anyone would guess.

A clogged filter. Same problem, indoor side. A choked filter starves the indoor coil of air, the coil runs too cold, and it either trips a safety or freezes into a block of ice. Frost on the copper lines at the furnace, or water on the floor around it, is the tell. Shut the system off, let it thaw completely, replace the filter, and try again. If it refreezes, there's more going on, and it's covered in why your AC freezes up.

Low refrigerant. Refrigerant doesn't get consumed. If it's low, it leaked, and a low charge makes the system cool poorly, ice up, and work harder than it should. This one has usually been developing all summer and finally crosses the line where the house won't hold temperature on a hot day. Not a DIY item. Finding the leak, repairing it, and weighing in the correct charge is a gauges-and-license job. If someone offers to top it off every August without finding the leak, that's a treadmill, not a repair.

The compressor. The expensive one, and thankfully the least common. Compressors mostly die from heat, and heat comes from all of the above — a dirty coil, low charge, a weak capacitor forcing hard starts. When one goes on an older unit, the repair-or-replace conversation gets serious in a hurry.

What to Check Before You Call

I'd rather you spend ten minutes on this list than pay for a truck to come diagnose a tripped breaker.

• Thermostat. Set to Cool, set below the room temperature, batteries fresh if it takes them. You'd be surprised how often that's it.
• Breaker. Check the panel for a tripped breaker for the outdoor unit and the furnace or air handler. Reset it once. If it trips again, stop — read why an AC keeps tripping the breaker and call, because repeated trips mean something electrical is wrong.
• Filter. Hold it up to a light. Can't see through it? Replace it.
• Outdoor unit. Is the fan spinning? Is the coil matted with debris? Did someone bump the disconnect switch on the wall next to it? Is anything piled against it?
• Ice. Look at the copper lines where they enter the furnace or air handler. Frost means shut it off and let it thaw for a few hours before anyone runs it.
• Airflow at the vents. Warm air blowing means one thing, no air blowing means another. Warm air from the vents has its own list of causes.

If everything checks out and it's still not cooling, that's a call. And if it's humming, buzzing, clicking without starting, or you smell anything electrical, shut it off at the thermostat first. Forcing a system through those symptoms is how a capacitor repair becomes a compressor replacement.

Limp, Repair, or Replace: The Late-Season Math

In June, you fix the air conditioner because there's a whole summer ahead. In late August the question changes: how much cooling season is left, and what's it worth to you?

Around here, the honest answer is a couple of weeks. Maybe three. West Michigan usually throws a few more hot days at us in early September, then the nights drop into the 50s and the equipment gets a break until next June.

When it's an easy repair, fix it. Capacitor, contactor, a cleaning, a thermostat. These are modest, and a system under twelve years old with a fresh capacitor is going to give you years more. Don't nurse a humming unit for two weeks to avoid a part that costs less than a nice dinner out.

When it's a big repair on an old unit, slow down. A compressor or a major refrigerant repair on a system that's fifteen years or older is where I'll usually tell you not to spend the money in August. You'd be putting a large repair into a machine that's near the end anyway, to buy two weeks of cooling. Turn on the fans, open the windows at night, and use the fall to make a calm decision instead of a hot-afternoon one. The repair-or-replace guide walks through the math in detail.

When it's in between, think about next June. A system that's twelve to fifteen years old with a moderate repair is a judgment call. What I'd ask is this: if you fix it now, do you trust it to start on the first 90-degree day next year? Because if the honest answer is no, you're going to be back in the same spot in June with every shop in the county slammed. Fixing it now and planning replacement for the off-season is a reasonable path. So is skipping the repair and replacing in the fall, when installers have open calendars and you can take your time comparing quotes.

I had one of these in Hudsonville earlier this month. Sixteen-year-old unit, compressor overheating on a coil that was half-blocked and a capacitor reading well under spec. The cleaning and the capacitor would have gotten it running again for a couple hundred dollars, and it would probably have finished the summer. But the compressor was drawing amps that told me it wouldn't be starting next June. So I gave them both options and told them which one I'd pick in their house. They took the cheap fix to finish the season and booked a replacement quote for October, which is how I'd have played it too.

Don't Let September Erase It

The trap with a late-August failure is that it seems to fix itself. The weather breaks, the AC isn't needed, and by October nobody remembers that it hummed and died on Labor Day weekend. Then the first hot week of June comes around and it doesn't start.

If your system struggled this month, whether it quit outright or just couldn't hold temperature on the hot afternoons, get it looked at before the season closes. September and October are the easiest weeks of the year to get a convenient AC repair appointment. The diagnosis is the same as it would be in June, and the fix is almost always cheaper than the version that waited ten months and failed on the busiest day of the year.

Members of our Comfort Plan get priority scheduling, 15% off repairs, and no overtime charges when the failure happens at a bad hour, and late-August failures are almost always at a bad hour. And if you'd rather have us go over the system before winter and give you an honest read on whether it'll make it another year, AC maintenance in September is a quiet, unhurried way to find out.