Your air conditioner is working — cool air is coming from the vents, the outside unit is running. But the thermostat says 78° when you set it to 72°, the system never shuts off, and by late afternoon the house is losing ground. This is a different problem from an AC that blows warm air and cools nothing at all, and it's diagnosed differently.
On a 95°+ day in Livermore, Pleasanton, or "not cooling enough" is one of our most common calls. Sometimes it's a real fault costing you capacity; sometimes it's a system doing exactly what it was designed to do against a load it was never sized for.
How it usually shows up:
- The AC runs nonstop all afternoon and never satisfies the thermostat.
- The house holds around 78–80° no matter where you set it.
- Some rooms cool fine and others — usually upstairs or sun-facing — stay hot.
- The air from the vents is cool, but not cold, and the electric bill has climbed.
First, the honest expectation
A residential air conditioner is typically sized to pull the indoor temperature down roughly 20°F below the outdoor temperature — that's the split it's built for, not an unlimited cold-making machine. So on a 105° inland afternoon, a healthy system holding the house near 85° is working correctly; at 95° outside, around 75° indoors is realistic. A system that runs constantly through the hottest week of the year but holds a reasonable split and catches up in the evening may have nothing wrong with it.
What is not normal: losing ground on a mild 80° day, a split clearly worse than last summer, or one part of the house staying hot while the rest is comfortable.
Why your AC can't keep up
When a system genuinely lost capacity, it's usually one of these — roughly in the order we find them:
- Low refrigerant from a leak. The most common capacity killer. AC doesn't consume refrigerant, so a low charge means a leak. An undercharged system still blows cool air, just less of it. Licensed-tech only (EPA 608).
- A dirty condenser coil. Caked with cottonwood and dust or blocked by shrubs, the outdoor coil can't reject heat and capacity drops — a big one inland, where summer dust is relentless.
- A dirty evaporator coil or clogged filter. Restricted airflow cuts cooling directly and can freeze the indoor coil solid. The cheapest and most common contributing cause.
- Leaky or undersized ducts. Very common in older Bay Area homes: ductwork in a 130° attic dumps the cooling you paid for into the attic. Usually shows up as "the upstairs never cools."
- An undersized system. A unit that was adequate before an addition or a converted attic bedroom can't cover the load on peak days.
- Heat gain the system can't out-run. Unshaded west-facing glass and thin attic insulation can add more heat than the AC removes during the worst hours.
- A weak or failing capacitor. A degraded run capacitor lets the compressor start but run inefficiently, quietly costing capacity.
- A thermostat in a bad spot. On a sun-hit wall or near a kitchen, it reads hotter than the house and calls for cooling forever.
The usual fix
Our tech starts with the two things behind most weak-cooling calls: airflow and refrigerant charge. We measure the temperature split across the indoor coil, check static pressure, and read the charge against spec. From there it's usually one of a few paths: clean a fouled condenser or evaporator coil, repair a refrigerant leak and recharge, replace a weak capacitor, or identify duct leakage bleeding off capacity before it reaches the rooms. If the system is simply undersized, we'll tell you that plainly rather than sell a repair that won't change anything. You get a firm quote before any part goes in.
DIY vs. calling a pro — the honest version
Safe to check yourself first (free):
- Change the air filter. A clogged filter is the number-one cause of lost capacity and costs a few dollars to rule out.
- Clear the outdoor condenser. Pull weeds, trim shrubs back for about 2 feet of clearance, and rinse off cottonwood or dust with a gentle hose spray (power off).
- Close blinds on sun-facing windows in the afternoon. On a 100° day this alone can be worth several degrees.
- Confirm every supply register is open and return grilles are clear. Closing vents in unused rooms does not help — it raises static pressure and hurts the whole system.
- Check where your thermostat lives. If afternoon sun hits it, it's lying to the system.
Call a pro when:
- The house loses ground on a moderate day, not just during a heat wave.
- Cooling is clearly worse than last season with a clean filter installed.
- You see ice on the copper line or indoor coil — that's low refrigerant or airflow.
- Some rooms never cool while others do (points to duct leakage or balance problems).
- You suspect low refrigerant. Topping off without finding the leak is illegal to vent and a waste of money.
Refrigerant, capacitors, and sealed-system work carry high pressure and line voltage — this is where a licensed tech pays for itself.
What it costs in the Bay Area
AC repairs vary widely by the part. In our pricing, a capacitor runs about $120–$350 — the cheap, common fix. A refrigerant leak repair plus recharge is roughly $180–$650 depending on the leak, and a compressor is the high end at $900–$1,600. Coil cleaning and duct work are quoted after we see the system. We charge a diagnostic fee that's credited toward the repair when you approve the work, and you'll always see a flat, upfront price before we start — no surprise line items.
Get your AC keeping up again
Triton repairs central AC, heat pumps, and mini-splits across the Tri-Valley, East Bay, and Peninsula — Livermore, Pleasanton, Dublin, San Ramon, and Hayward, where inland summers hit hardest. Same-week (often same-day) appointments and licensed techs.
Book online or call (888) 993-5699. We'll measure the system and tell you honestly whether it's a fault or a load problem.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- AC Not Cooling / Blowing Warm Air — when there's no cooling at all
- AC Can't Keep Up During a Heat Wave — peak-day expectations
- Weak or No Airflow From Vents — the airflow side of the problem
- HVAC & AC Repair in Livermore — Tri-Valley service area
Frequently asked questions
Why does my AC run constantly but never reach the set temperature? Usually the system has lost capacity — low refrigerant from a leak, a dirty condenser or evaporator coil, a clogged filter, or leaky attic ducts. It can also be an undersized system or heavy afternoon heat gain. Start with a fresh filter and a cleared outdoor unit; if it still can't catch up, the charge and coils need measuring.
Is it normal for an AC to run all day in a heat wave? Yes. Air conditioners are sized to hold roughly a 20°F split from the outdoor temperature, so on a 105° inland afternoon a healthy system may run continuously and still only hold the house near 85°. Losing ground on a mild day is the sign of a real fault.
Why is my upstairs hot while downstairs is cool? Heat rises, and upstairs rooms sit under a hot attic with the longest duct runs. Leaky or undersized ductwork in that attic is the most common cause, along with sun load through upstairs windows. A tech can check duct leakage and airflow balance to the affected rooms.
How much does it cost to fix an AC that isn't cooling enough in the Bay Area? It depends on the cause: a capacitor is about $120–$350, a refrigerant leak repair and recharge runs roughly $180–$650, and a compressor is the high end at $900–$1,600. Coil cleaning and duct repairs are quoted on-site. We credit the diagnostic fee toward the repair and give you a firm price before any work begins.
Does closing vents in unused rooms help the rest of the house cool? No. Closing registers raises static pressure, which reduces total airflow, hurts efficiency, and can freeze the indoor coil. Leave all supply and return vents open and address the actual capacity or duct problem instead.