Top 5 Reasons Your AC Isn’t Working

When a Trusted Heating & Air technician answers a no-cooling call, the check runs in one direction: a dirty filter first, then a blocked condensate line in the attic, then clogged condenser coils, then a failed capacitor, and finally a failing condenser fan motor. That’s the order a technician works the call, starting with the cheapest and most visible causes and working toward the electrical, not a ranking of how often each one happens.

It’s also not the list most “why isn’t my AC working” articles run: thermostat, breaker, low refrigerant, ductwork. Only one of our five, the filter, shows up on that generic list. The other four come from the technician who has spent more than a decade running these specific no-cooling calls across Collin County, and one of them, the condenser fan motor, we haven’t seen named on a competitor’s page. We make money on all five of these repairs, which is exactly why it’s worth saying plainly: two are simple enough to check yourself, one is DIY only if you’re comfortable working around live electrical, and one, the capacitor, we’d rather you leave to us. Rule out the two free checks below before you look at same-day AC repair.

Check the thermostat and breaker first

Before any of the five below, check the thermostat and the breaker. Confirm it’s set to cool, the set temperature is below room temperature, and the batteries aren’t dead if it uses them. Then check the breaker panel for anything tripped. Both take under a minute and catch a real share of dead-system calls, free. It matters here specifically because a tripped float switch, covered next, can shut a system down in a way that looks exactly like a blank or unresponsive thermostat. If the thermostat and breaker check out and the system is still doing nothing, or running without cooling, work through the list below in order.

Start with the filter

Pull the filter and hold it up to a light. If you can’t see light through it, that alone can starve airflow badly enough to mimic weak cooling, a frozen coil, or a system that runs constantly without ever hitting the set temperature. It’s free, it takes about thirty seconds, and it’s a homeowner job every time.

One caveat: if you see ice on the indoor coil or the refrigerant lines when you check the filter, don’t just swap the filter and switch cooling back on. Set the thermostat to fan-only, or off, and let the coil thaw completely first, which can take a few hours, then replace the filter and try cooling again. Running the system against a frozen coil can damage the compressor.

Check for a blocked condensate line in the attic

Most North Texas homes run the air handler in the attic, so when its condensate drain clogs, a float switch trips to keep water from overflowing the pan. Depending on how your system is wired, that can cut off cooling only or shut down the whole unit, so don’t assume it’s one or the other. The visible tell, if it’s gone on long enough, is a stain on the ceiling below the attic air handler.

You can safely clear the outdoor end yourself: find where the line terminates outside, often a PVC pipe near the condenser or the foundation, and clear it with a wet/dry vac. Getting into the attic to work on the line itself means stepping across joists through ceiling drywall that isn’t decked to walk on, and that’s a real way to put a leg through a ceiling. If clearing the outdoor end doesn’t reset the float switch, that’s a technician’s job, not a ladder and a flashlight.

Look at the condenser coils for buildup

Once you’re outside at the unit, clogged coils are the easiest failure to spot with no tools: grass clippings, cottonwood fluff, and pollen packed into the fins. The tell is a system that runs constantly and never quite gets cold, because the coil can’t shed heat with its airflow blocked.

Rinsing the outside of the cabinet helps, but that’s not where most of the buildup collects. Getting the coil properly clean usually means removing the top cover or grille, a step most competitors’ advice skips. That’s still homeowner work, with rules that matter. Power off at the breaker and the outdoor disconnect before you remove a single screw. The fan is bolted to that top panel and stays wired in, so don’t disconnect the wiring: lift the panel only far enough to clean behind it, have someone hold or prop it, and never let it hang by the wires. Don’t open the separate electrical access panel either, that’s a different job. Rinse with a garden hose on a normal spray pattern, working from the inside out, and skip the pressure washer: the fins bend at very low pressure and won’t un-bend. If you use a coil cleaner spray, wear gloves and eye protection and follow the can’s dilution and rinse instructions.

Our AC maintenance and tune-up checklist covers coil cleaning as part of a seasonal routine, before it turns into a summer breakdown.

Test the capacitor before touching anything else

If the coils are clean and the system still won’t cool, or the outdoor unit hums without spinning up at all, the capacitor is next, checked with a meter before anything gets condemned. A humming outdoor unit gets blamed on a dying compressor more often than it deserves; in our experience the capacitor is the actual cause more often, since it takes the hardest heat and electrical stress of any part in the cabinet.

This is the one item on this list we won’t walk you through testing or replacing yourself. A capacitor can hold a shock-level charge even with the breaker off, since it’s built to store energy, not release it the moment power stops. There’s no safe amount of time to wait it out, and no way to tell whether one is still charged by looking at it. If anything, a capacitor is more likely to be holding a dangerous charge in this exact failure, since charge normally bleeds off through an intact motor winding, and a failed capacitor often comes paired with one that isn’t intact anymore. Our guide on how to tell if an AC capacitor is bad covers the signs in more depth. Here, the verdict is simple: if you suspect the capacitor, call someone.

Check the condenser fan motor last

Only get here once the capacitor has tested good and the fan still isn’t turning right, since condemning a motor before ruling out the cheaper part makes a repair more expensive than it needs to be. The condenser fan motor is a failure we don’t see named on other companies’ lists, but it turns up often enough in our calls to matter.

Before you touch the fan, pull the outdoor disconnect, the gray box mounted at or near the condenser (turning the thermostat off isn’t the same thing), and confirm the breaker is off too. Then use a stick or a screwdriver handle through the grille to test whether the blade turns freely, never your fingers. Don’t open the separate electrical access panel to do this: that’s where the capacitor lives, and it’s not part of this check.

What you feel tells you which part is failing. A blade that spins freely by hand but won’t run on its own usually points back to the capacitor, so if you land here, it’s worth confirming that part tested good. A blade that’s stiff or hard to turn points to worn motor bearings, and a motor in that state is often weeping oil, a sign technicians look for in the field, and a separate issue from a refrigerant leak or a compressor oil leak. Diagnosing either outcome is safe from the driveway. Replacing the motor is DIY only if you’re genuinely comfortable working around live electrical, not just handy.

If what you’re seeing doesn’t match any of these five, our AC repair symptom guide walks through diagnosis by what your system is doing, not by what’s statistically likely.

We make money whether the fix is a filter or a fan motor, which is why we’d rather tell you which two of these five you can check yourself for free. Schedule a diagnostic visit or call (945) 333-4822, and Trusted Heating & Air Conditioning’s EPA Section 608 certified technicians will test the actual part, capacitor included, before anything gets replaced, under our active TDLR Air Conditioning/Refrigeration Contractor license (TACLA152199C, active through June 2027).