There’s a particular kind of frustration I hear in people’s voices on the phone, and it goes something like this: it’s been quitting on us for two weeks, it did it three times yesterday, and now that you’re on your way it’s running like it’s brand new. I’m sorry to waste your time.
You’re not wasting my time. That’s a real problem, it has a real cause, and the fact that it isn’t performing on demand doesn’t mean I can’t find it. Intermittent faults are honestly some of the more interesting work I do, and I want to explain how they get diagnosed, because homeowners in Red Oak often assume the only option is to wait until the thing dies for good.
Why it always behaves when help arrives
It isn’t bad luck and it isn’t the machine being contrary. Nearly every intermittent fault is a component that works fine in ordinary conditions and gives up when conditions push it past its margin. Change the conditions and the symptom goes away.
Think about what’s different when I show up. Your system has usually been off for a while because you shut it down, so everything in the cabinet has cooled off. A component that’s marginal when it’s hot may be perfectly fine at 90 degrees instead of 150. The attic hasn’t had all afternoon to bake. The compressor hasn’t been running for six straight hours. The outdoor temperature might be twelve degrees lower than it was at four o’clock yesterday when the thing quit.
So the machine isn’t lying to me. It’s telling me the truth about right now, and right now happens to be conditions where it works. That’s actually useful information, because it narrows things considerably. A part that fails only under load and heat is a different suspect list than a part that’s failed outright.
Faults leave evidence, and the evidence stays
Here’s the part people don’t expect. A component doesn’t fail cleanly out of nowhere. It degrades, and degradation leaves marks that don’t disappear just because the system happens to be running at the moment I’m standing there. Reading those marks is most of the skill in this work.
Some of what I’m looking for:
- Heat discoloration. Wire insulation that’s turned brown or brittle, a scorched spot on a terminal, a control board with a darkened area around a relay. Heat that severe doesn’t happen during normal operation. Something has been running hot repeatedly, and the color is a record of it.
- Pitted or welded contactor points. The contactor is the electrical switch that starts your compressor, and every time it closes there’s a small arc. When it’s tired, those points pit, then carbon up, then start making poor contact intermittently. Pull the cover, look at the points, and you can often see the whole story. A contactor that’s arcing badly will drop out and back in under load, which is exactly the “it quits and then it comes back” symptom people describe.
- A capacitor reading marginal but not dead. This is the single most common cause of an intermittent no-start I find. A run capacitor rated at 45 microfarads that’s measuring 37 might still get the compressor going on a mild morning and completely fail to on a 101-degree afternoon when the motor needs more help. It’s a bad part right now, and it reads bad right now, even though the system is running.
- Bulged or leaking capacitor cans. A dome on the top or oily residue at the base means it’s on its way out regardless of what today’s number says.
- Corrosion at connections. Green or white crust on a terminal adds resistance, resistance makes heat, heat makes more corrosion. That loop runs for months before it finally opens up.
- Rodent damage and rub-through. Wiring chewed to the copper or worn where it crosses a sheet metal edge. That can short intermittently with vibration and look like a ghost.
The wiggle test, and why I do it on purpose
One of my most useful tools costs nothing. With the system running and my meter reading, I go through the low-voltage and line-voltage connections and physically move them. Tug the wire at the terminal. Flex the harness where it enters the cabinet. Press on a connector.
If a reading jumps or the system hiccups when I move something, I just reproduced your intermittent fault on demand, and I know exactly where it lives. Loose spade connectors are a genuinely common cause of the mystery shutdown, because a connector that’s backed off a hair makes contact until vibration or thermal expansion breaks it, then makes contact again when things settle. It’ll pass every visual inspection in the world.
I do the same thing on the thermostat wire. A staple driven a little too far somewhere in the wall, a splice in the attic that’s corroded, a wire run against something sharp. A momentary open in that low-voltage circuit shuts the whole system down and then it starts right back up, and the homeowner is left thinking the equipment is haunted.
Why Red Oak sees a lot of this
Red Oak’s been one of the fastest-growing corners of Ellis County for years, and the housing timeline is unusually wide for a town its size. There are established neighborhoods from the eighties and nineties, and there are subdivisions where the sod lines still show.
Both ends of that spectrum generate intermittent faults, for different reasons. The newer homes are hitting the window where builder-grade equipment starts asking for attention, generally ten to fifteen years in, and the first thing to go on a builder-grade system is usually one of the cheap electrical components. Capacitors and contactors on those units are picked to hit a price, and North Texas summers work them harder than the spec sheet ever imagined. They rarely die all at once. They get flaky first.
The established neighborhoods are on their second or third system generation, which means somebody has been in that cabinet before. Every service visit and every changeout is another chance for a connection to get reused, a wire to get routed against an edge, or a terminal to get crimped a little loose. Older wiring in an attic that’s cycled between 40 degrees and 140 degrees a few thousand times gets brittle. None of that shows up until conditions stack the right way.
What you can do to help me catch it
The most valuable thing a homeowner can hand me on an intermittent call is a record. Not a technical one. Just notes.
- Write down the time of day it happens. Late afternoon points hard at heat and load. First thing in the morning points somewhere else entirely.
- Note the outdoor temperature as best you can, or at least whether it was one of the hot days.
- Describe what it does, precisely. Does the whole system go dead and quiet? Does the indoor blower keep running while the outdoor unit stops? Does it blow air that isn’t cold? Those are three different failures and they narrow the list a lot.
- Note how long until it recovers. A system that comes back in exactly five or ten minutes is behaving like something on a timer or a thermal overload resetting. A system that stays down until you flip the breaker is telling a different story.
- Check whether the breaker tripped or the system just stopped. Big distinction.
You can also look at your filter and make sure your registers are open, because an airflow restriction can cause an overload to trip intermittently and it’s the one thing on this list you can fix yourself for a few dollars.
Where your part ends: don’t open the electrical compartment. The capacitor in there holds a charge after the power is off and it can hurt you badly. Watching, writing down, and changing a filter is the whole homeowner half of this job, and it’s genuinely valuable.
When the honest answer is monitoring
Sometimes I go through everything and find nothing conclusive. It happens. In that case I’ll tell you so rather than picking a part and swapping it to look decisive.
What I’d do instead is leave the system with the things I did find corrected, tell you exactly what to watch for, and set the expectation that if it recurs we’ll catch it with more information than we had this time. On some systems there’s a fault history stored in the control board that I can read out, and on those the board has been quietly keeping the record for us the whole time.
What I won’t do is start replacing components on a hunch and charging you for each one until the symptom happens to go away. That approach can run through several parts before it lands, and half the time the problem comes back anyway because nothing that got replaced was ever the cause.
Don’t wait for it to fail completely
The instinct with an intermittent problem is to live with it until it becomes constant, because at least then somebody can find it. I understand the logic and I’d still push back on it. Flaky electrical components put stress on expensive ones. A contactor that’s chattering makes the compressor start and stop far more often than it should, and a capacitor that’s out of spec makes the compressor motor work harder every single time it comes on. Give either of those a whole summer and the small problem can take the big part with it.
You can read more about how we handle AC repair, see everything we cover around town on the Red Oak service page, or look at real jobs in the gallery. If it’s easier to write it out, send us the details and the notes you’ve been keeping.
If your system has been acting up and quitting right when you need it most, call or text (214) 717-3959 to Book a Service Call. Bring me your notes and I’ll read the evidence the fault left behind, whether or not it decides to perform while I’m there.
