It's 5 p.m., it's 106° outside, and the thermostat says 81 and climbing. The AC is running. It's been running all day. So why isn't the house cooling down?
First, some perspective. On the very hottest days, even a healthy, correctly sized air conditioner in the Sacramento Valley may struggle to hold 72°. Most residential systems are designed to keep the inside about 20 degrees cooler than the outside, and a typical design day for our area is in the high 90s or low 100s. So if it's 108° and your house is sitting at 80, your system may be doing exactly what it was built to do.
But if your house is getting warmer every hour, the air from the vents feels lukewarm, or the system struggled even on a 95° day, something else is going on. Here are the seven causes we find most often.
1. A dirty air filter
It sounds too simple, but it's the most common cause we see. A clogged filter starves your system of airflow, which reduces cooling and can even freeze the indoor coil. During summer, especially with pets or smoke in the air, filters can load up in just a few weeks.
What to do: Pull the filter and hold it up to the light. If you can't see through it, replace it.
2. A dirty outdoor coil
Your outdoor unit's job is to dump the heat it pulled out of your house. When its coil is coated in dust, cottonwood fluff, and grass clippings, it can't do that well, especially when the outdoor air is already 105°. Pressures rise, efficiency falls, and parts work harder.
What to do: With the power off at the disconnect, gently rinse the coil with a garden hose (no pressure washer). Keep plants and fences at least two feet away from the unit.
3. A failing capacitor
Capacitors give the compressor and fan motor the boost they need to start and run. Heat breaks them down over time, and a weak capacitor can make the system run poorly long before it fails completely. It's the single most common part we replace in the summer.
What to do: If you hear the outdoor unit humming but the fan isn't spinning, turn the system off and call for service. Running it that way can overheat the compressor.
4. Low refrigerant from a leak
Air conditioners don't "use up" refrigerant. If it's low, there's a leak. Low charge reduces cooling capacity and can cause ice to form on the lines or coil.
What to do: If you see ice on the copper lines, turn the cooling off, leave the fan on to thaw the coil, and call us. Ask your technician about finding the leak, not just topping it off.
5. Leaky or disconnected ductwork
In many Elk Grove and Sacramento homes, ducts run through attics that hit 140° or more. If a duct is torn or disconnected, you're pouring cold air into the attic. One room barely getting any air is a classic sign.
What to do: If it's safe, take a look in the attic for crushed or disconnected ducts, or have us inspect them. See our ductwork services.
6. An undersized or aging system
If your system was undersized from the start, or your home has changed (an addition, a converted garage, new windows), the AC may simply be too small. Systems also lose capacity as they age, especially past 15 years.
What to do: Have a technician measure the system's performance. If it's healthy but still can't keep up, a load calculation will tell you whether it's the right size for your home.
7. Heat getting in through the house itself
West-facing windows, thin attic insulation, and poor attic ventilation all add heat faster than your system can remove it on peak afternoons.
What to do: Close blinds on the sunny side in the afternoon, consider solar screens on west windows, and check your attic insulation level.
Tips to help your AC on the hottest days
- Pre-cool the house in the morning, then let the temperature drift up a little in the late afternoon.
- Don't drop the thermostat to 65 to "catch up." It won't cool faster.
- Avoid running the oven and dryer in the afternoon.
- Use ceiling fans to feel a few degrees cooler.
- Keep interior doors open so air can return to the system.
When to call a professional
Call us if the air from your vents is warm, you see ice, the outdoor fan isn't spinning, the breaker trips, or your house keeps getting warmer even after you've replaced the filter. The sooner a struggling system is checked, the less likely a small problem becomes a compressor replacement. Learn more about our AC repair service, or call (916) 800-3076.