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When temperatures in the Inland Empire climb into the triple digits, your air conditioner earns its keep. But there is a difference between an AC that works hard on a scorching afternoon and one that simply never stops running. If your system is cycling on and stays on for hours without shutting off, something is wrong. Left unaddressed, a constantly running AC drives up your energy bills, puts unnecessary wear on your equipment, and can eventually lead to a breakdown at the worst possible time.
The good news is that there are several well-known reasons an AC runs nonstop, and most of them are diagnosable and fixable. Here is what to look for.
What Does It Mean for an AC to Run Constantly?
On the hottest days of the year, your AC may run in longer cycles than usual. That is normal. What is not normal is a system that runs for hours on end without ever reaching the thermostat's set temperature, or one that cycles on and stays on regardless of how cool the house feels. If your AC is running but the house is not getting comfortable, or if the system seems to never shut off even on a mild evening, the system is struggling with something.
Common Reasons Your AC Won't Stop Running
1. A Dirty or Clogged Air Filter
This is the most common and most preventable cause. When the air filter is clogged with dust, pet hair, and debris, airflow through the system is restricted. Your AC has to work harder and longer to pull enough air across the evaporator coil, and the result is a system that runs longer cycles to achieve the same cooling output. In high-use summer months, filters can clog faster than homeowners expect, especially in households with pets, multiple occupants, or ongoing home improvement projects. Check your filter first. If it is visibly gray or packed with debris, replace it and see if the issue improves.
2. Low Refrigerant
Refrigerant is the substance that makes cooling possible. It absorbs heat from the air inside your home and releases it outside. When refrigerant levels are low, the system loses its ability to transfer heat efficiently and has to run longer to achieve any meaningful cooling. Low refrigerant is always the result of a leak, not normal depletion. A licensed technician needs to locate the leak, repair it, and recharge the system. Simply adding refrigerant without fixing the leak is a temporary patch that will not solve the underlying problem.
3. A Dirty Evaporator or Condenser Coil
Your AC has two sets of coils: the evaporator coil inside the air handler and the condenser coil in the outdoor unit. Both need to be reasonably clean to transfer heat effectively. The outdoor condenser coil in particular is exposed to dust, leaves, grass clippings, and other debris year-round. When coils are heavily coated, heat transfer suffers and the system runs longer cycles trying to compensate. Dirty coils are one of the primary reasons regular maintenance matters, as technicians clean the coils during a tune-up to restore efficient operation.
4. An Undersized Air Conditioner
An AC that is too small for the space it is cooling will run nearly continuously because it never has enough capacity to actually reach the set temperature. This can happen when a system was improperly sized at installation, or when a home has been expanded since the original system was put in. If your system runs nonstop even when temperatures are moderate and you have always had trouble keeping the house cool, undersizing may be the root cause. A load calculation by a qualified technician will confirm whether the system is appropriately sized for your home.
5. Thermostat Issues
Sometimes the problem is not the AC at all. A thermostat that is reading the temperature inaccurately, is located in a drafty or sun-exposed spot, or is simply malfunctioning can cause the system to run longer than necessary. If the thermostat thinks the house is warmer than it actually is, it will keep calling for cooling. Try checking whether the thermostat location is near a heat source, a window, or a vent, any of which can throw off readings.
6. Leaky or Poorly Sealed Ductwork
If your ducts are leaking conditioned air into unconditioned spaces like the attic or crawlspace, a significant portion of your system's cooling output is being wasted before it ever reaches the living areas. The result is a system that runs constantly trying to meet a demand it cannot satisfy. Duct issues are common in older homes and can account for substantial energy waste. A duct inspection can identify whether leakage is contributing to the problem.
What You Should Do
Start with the basics. Replace the air filter if it has not been changed recently and make sure all vents in the home are open and unobstructed. Check the outdoor unit for visible debris or damage. If those steps do not resolve the issue, the next move is to schedule a professional inspection. A qualified technician can check refrigerant levels, test the thermostat, inspect the coils, and evaluate the ductwork.
Catching the problem early matters. A system that runs nonstop is under constant mechanical stress, and components that are already working overtime are more likely to fail. Addressing the root cause now is almost always less expensive than waiting for a breakdown mid-summer.
Schedule a Service Visit Today
If your AC is running nonstop and you are not sure why, Sheldon's Heating, Air Conditioning & Plumbing is here to help. Our technicians serve homeowners throughout Corona, Riverside, Ontario, San Bernardino, and Moreno Valley and can diagnose the issue quickly so you can get back to a comfortable home. Call us at (951) 574-2226 or reach out online to schedule your appointment today.