AC Not Cooling
Weak cooling is easy to shrug off for a day, but ride it out through a San Antonio July and a system that is a few degrees behind becomes a system that never catches up. Every hour it labors to close a gap it cannot close piles more runtime onto the compressor - and a compressor pushed for weeks in triple-digit heat is how a modest repair turns into a full replacement.
Cooling comes down to moving heat from one place to another. Refrigerant soaks up heat from the air inside your home at the indoor coil, then releases it outside at the condenser. For that cycle to actually drop your temperature, three things have to hold at once: enough air moving across the indoor coil, enough refrigerant at the right pressure, and a condenser that can shed the heat it collected. When cooling goes weak, one of those three has usually slipped. The equipment still hums and pushes air, but the heat it picks up inside is not making it all the way outside, so the house stalls a few degrees above your setting.
Some of what causes this you can rule out in ten minutes. A filter so loaded it is starving the coil of air, supply vents closed off in half the rooms, or a condenser choked by grass clippings and mulch are quick fixes. The real repairs sit deeper: a refrigerant charge that has bled down through a leak, a compressor losing its pumping strength, a run capacitor too weak to spin the motors up to full speed, or ductwork bleeding cooled air into the attic. Telling the ten-minute checks apart from the technician-level faults is the entire point of a diagnosis, because from your thermostat they feel identical.
South Texas stacks the deck against a coasting system. The Edwards Aquifer water that serves most of the metro is genuinely hard, and the mineral scale it leaves behind coats coils and narrows drain lines, quietly cutting how well the system trades heat. Then there is the runtime - during a triple-digit stretch the overnight low barely dips, so your AC never gets the cool hours a system in a milder climate leans on to recover. It runs nearly around the clock for weeks. Add cedar and oak pollen packing the outdoor coil, and a unit that was only a little behind in June can fall badly behind by August.
Signs it's this, not something else
- Air still blows from the vents but is only a few degrees cooler than the room - genuinely warm air points instead to a lost charge or a dead condenser
- The house holds steady a few degrees above the setting rather than climbing quickly
- Runtime is long and nearly constant, and your electric bill has crept up
- Some rooms cool while others do not, hinting at duct or airflow loss rather than a whole-system failure
- No ice on the lines and no water on the floor, which would steer you toward a frozen coil instead
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Frequently asked questions
Is this the compressor or just a capacitor?
From inside the house you cannot tell - both leave you with weak, longer-running cooling. The difference matters for your wallet, though: a capacitor is a small, common part, while the compressor is the most expensive component in the system. A technician measures the motor's startup draw and the system pressures to say which one is truly failing before anything is replaced.
How long can I wait before this does real damage?
If the air is still somewhat cool you have a little time, but do not let it run through a heat wave. A system fighting low charge or poor airflow works hotter and longer, and weeks of that in San Antonio heat is exactly what wears out a compressor. Getting it looked at within a few days is far cheaper than waiting until it quits entirely.
Could it just be the heat, and the AC is actually fine?
A healthy system in good shape should hold your set temperature even on a 100-degree afternoon, though it may run almost nonstop to do it. If yours cannot keep up and the gap keeps widening, that is not just the weather - something in the airflow, the charge, or the condenser has slipped and is worth checking.
Why does it cool at night but fall behind in the afternoon?
When the outdoor temperature climbs, the condenser has a harder time rejecting heat, so a system that is already marginal - low on charge or dirty - only falls behind during the hottest hours. Cooling fine overnight but losing ground by mid-afternoon is a classic sign the system is sitting right on the edge of its capacity.
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