Why Your AC Runs Constantly and What to Do About It

If your AC never seems to shut off, you're right to wonder what's going on. An air conditioner that runs constantly is one of the most common AC problems Austin homeowners report, and it can mean anything from "totally normal" to "you need a technician yesterday." The key is knowing the difference. Here's how to tell when constant running is expected, when it signals a problem, and what you can do about it.

When Constant Running Is Normal

In Austin, there are times when your AC running nonstop is actually expected behavior. Understanding these situations can save you from unnecessary worry and service calls.

Extreme Heat Days

When outdoor temperatures exceed 100 degrees, your AC may run continuously for hours. Austin regularly sees 30 to 69 days above 100 degrees each summer. On those days, your system is fighting against extreme heat load. It's designed to run until it reaches your set temperature. If it's 105 outside and you've set the thermostat to 74, the unit may not cycle off at all during the hottest part of the day. That's normal.

Thermostat Set Very Low

If you keep your thermostat at 68 or 70 when it's 95 outside, your AC will work much harder and longer. The greater the gap between outdoor temperature and your desired indoor temperature, the more the system has to run. There's nothing wrong with wanting a cool house, but understand that aggressive settings mean longer run times, especially in Central Texas.

Peak Afternoon Hours

Between roughly 2 p.m. and 6 p.m., when the sun is highest and your roof and walls absorb the most heat, your AC will run more than it does in the morning or evening. That's physics, not a malfunction.

New or Recently Serviced Systems

If you just had a new system installed or a professional tune-up, your AC might run more often at first. New systems are often sized to run longer cycles for better humidity control and efficiency. That's by design. Similarly, after a tune-up that improved airflow or refrigerant levels, the system may run differently than before. Give it a few days before assuming something is wrong.

When Constant Running Is a Problem

If it's 85 degrees outside and your AC never stops, something is probably wrong. Same goes for mild spring or fall days when the system should be cycling on and off. Here are the most common causes and what to do about each.

Dirty Air Filter

A clogged filter restricts airflow through your system. When airflow drops, the evaporator coil can't absorb heat efficiently. The system runs longer trying to reach the set temperature, and in severe cases, the coil may freeze, making things worse.

Solution: Check your filter monthly during heavy-use months. Hold it up to a light. If you can't see through it, replace it. This is the single most common fix for AC running constantly, and it takes five minutes.

Pro Tip: Buy filters in bulk before summer. When it's 100 degrees and your AC is struggling, you don't want to run to the store. Keep two or three extras on hand.

Low Refrigerant

Refrigerant is what absorbs heat from your indoor air. Your AC doesn't "use up" refrigerant. If levels are low, there's a leak. Low refrigerant means the system can't cool effectively, so it runs and runs without ever satisfying the thermostat.

Solution: A technician must locate and repair the leak, then recharge the system. Adding refrigerant without fixing the leak is a temporary fix that wastes money. If you suspect low refrigerant (ice on the lines, hissing sounds, or the system never reaching set point), schedule AC repair.

Undersized System

If your AC was sized too small for your home, it will run constantly trying to keep up. This often happens when a system was installed for a smaller space, after an addition, or when the original sizing was done poorly.

Solution: A load calculation can confirm whether your system is undersized. If it is, the only real fix is replacing the system with one that matches your home's cooling needs. Running an undersized unit constantly also shortens its lifespan and drives up your electric bill. Many Austin homeowners discover their system was undersized only after years of high bills and constant running.

Dirty Evaporator or Condenser Coils

Dust, dirt, and debris on the evaporator coil (indoor) or condenser coil (outdoor) reduce heat transfer. The system has to run longer to achieve the same cooling.

Solution: Coils should be cleaned during annual maintenance. Outdoor coils can be gently hosed off if they're accessible and not obstructed. Indoor coils require a technician to clean properly without damaging the fins.

Ductwork Leaks

According to the U.S. Department of Energy, duct leaks account for 20 to 30 percent of air loss in a typical home. If cold air is escaping into your attic or crawl space before it reaches your living spaces, your AC has to run longer to compensate. In Austin, where attic temperatures regularly exceed 140 degrees in summer, duct leaks are especially costly.

Solution: A duct leak test can identify problem areas. Sealing and insulating ducts improves efficiency and reduces run time. In some cases, sections of ductwork need replacement.

Thermostat Issues

A thermostat that's miscalibrated, placed in a hot spot (direct sunlight, near a lamp), or malfunctioning can tell the AC to run when it shouldn't. Smart thermostats can also glitch after updates or power outages.

Solution: Verify the thermostat is set to "Cool" and "Auto" (not "On" for the fan). Check that it's not in direct sunlight or near heat sources. If the display shows incorrect temperatures or the system ignores your settings, the thermostat may need recalibration or replacement.

Failing Compressor

A compressor that's losing efficiency will run longer to achieve the same cooling. You might notice the system running constantly while the house slowly gets warmer, or it never quite reaches the set temperature.

Solution: A technician can test compressor performance. If it's failing, repair or replacement depends on the age of the system. Compressor replacement is costly; for older units, full system replacement is often the better investment.

Poor Insulation or Air Sealing

If your home loses cooled air through gaps, poor insulation, or leaky windows and doors, your AC has to work harder to maintain temperature. The system runs longer because heat keeps infiltrating.

Solution: Improving insulation and air sealing reduces the load on your AC. This is a home improvement project, but it pays off in lower energy bills and less strain on your HVAC system.

Energy Cost Implications

An AC that runs constantly can double or triple your energy bills. Your cooling system is typically the largest single user of electricity in your home. When it runs 24/7 instead of cycling on and off, consumption spikes. In Austin, where electric rates and cooling demand are both high, that adds up fast.

A properly functioning system should cycle on and off throughout the day. On a typical 95-degree day, you might expect it to run 50 to 60 percent of the time. If it's running 90 percent or more, or never shutting off at all, something is wrong. The extra runtime translates directly to higher kilowatt-hours and a bigger bill at the end of the month.

If you've noticed a sudden jump in your electric bill and your AC seems to run nonstop, the two are likely connected. Fixing the underlying cause (filter, refrigerant, duct leaks, etc.) will reduce run time and bring your bills back down. In many cases, the cost of a service call pays for itself within a month or two through lower energy use.

When to Call a Professional

You can handle the filter yourself. For everything else, a licensed HVAC technician is the right call. Schedule service if:

1. Your AC runs constantly and never reaches the set temperature, even on mild days
2. You've replaced the filter and the problem persists
3. You see ice on the refrigerant lines or indoor coil
4. You hear unusual sounds (hissing, grinding, clicking) from the indoor or outdoor unit
5. Your electric bill has spiked and your AC runs nonstop
6. The system is more than 10 years old and has never had a professional tune-up

A technician can perform a full diagnostic, measure refrigerant levels, check airflow, and identify the root cause. At CG Service Pros, we provide upfront pricing and clear explanations. If a simple fix will solve it, we'll tell you. If the system is undersized or failing, we'll explain your options for repair versus replacement without pressure.

Austin-Specific Reality Check

On 100-plus degree days, systems may run continuously, and that's expected. Austin's climate pushes residential AC equipment to its limits. But if it's 85 outside and your AC never stops, something is wrong. Don't assume it's "just the heat." The difference between normal and problematic is whether the system eventually satisfies the thermostat and cycles off. If it doesn't, get it checked.

Regular maintenance before the heat arrives helps catch small issues before they become big ones. A tune-up includes cleaning coils, checking refrigerant levels, testing electrical components, and ensuring airflow is adequate. It's one of the best ways to keep your AC running efficiently and avoid the constant-run trap.

Quick Checklist Before You Call

If your AC runs constantly, run through this list first:

1. Filter: Is it dirty? Replace it and wait 24 hours to see if run time improves.
2. Thermostat: Is it set to Cool and Auto? Is the set point reasonable for the outdoor temperature?
3. Outdoor unit: Is it clear of debris, leaves, and vegetation? Is the fan spinning when the system runs?
4. Vents: Are supply and return vents open and unobstructed? Closing too many vents restricts airflow.
5. Weather: Is it over 100 degrees outside? If so, some constant running may be normal.

If you've checked all of these and the problem persists, or if you see ice, hear strange noises, or the house never reaches the set temperature, it's time to call a professional.

Get Your AC Running Right

At CG Service Pros, we serve homeowners across Austin, Round Rock, Cedar Park, Pflugerville, and the surrounding Central Texas area. If your AC runs constantly and you're not sure why, we'll diagnose the problem, explain it clearly, and fix it. No upsell pressure, no hidden fees. Just honest service from NATE-certified technicians.

Schedule AC Service Today

Have questions? Call us at (512) 766-5079 or visit our contact page to schedule service.