Your AC Is Running Constantly — Is That Normal or a Problem?
You check the thermostat, the AC is running, but the house still feels warmer than it should. You notice the outdoor unit hasn't shut off in hours. Is this just Missouri summer doing what Missouri summer does, or is something wrong with your system? The answer depends on a few things, and knowing what to look for can help you decide whether to wait it out or call for service.
When Constant Running Is Normal
On days when outdoor temperatures hit 95 degrees or above, an air conditioner may run for extended periods — even most of the day. That's not necessarily a problem. What matters is whether the system is reaching and maintaining your set temperature. If it's 95 outside and your home stays at 72, the system is doing its job even if it's running continuously.
The distinction to pay attention to: the AC runs all day AND the house never gets cool enough. That combination suggests a performance issue, not just a hot day.
Common Reasons AC Can't Keep Up
Several problems can cause an air conditioner to run without adequately cooling your home:
Dirty Air Filter
A clogged filter restricts airflow across the evaporator coil. Less air means less heat transfer, which means the system works longer to remove the same amount of heat. Start here — replace the filter and see if performance improves over the next day or two.
Low Refrigerant
Refrigerant doesn't deplete on its own. If your system is low, there's a leak. Low refrigerant reduces the system's cooling capacity significantly — it may run all day and barely cool the space. This requires a licensed technician to diagnose and repair. The Energy Star cooling system efficiency guidelines note that proper refrigerant charge is critical to efficient operation.
Dirty or Frozen Evaporator Coil
The evaporator coil absorbs heat from your home's air. If it's coated with dust or debris — or worse, frozen — it can't do that job efficiently. A frozen coil requires the system to be shut off to thaw before a technician can clean it.
Undersized Equipment
If your AC has always struggled on hot days — even in good repair — it may simply be undersized for your home. A load calculation by an HVAC technician can confirm whether your system is appropriately sized.
The Humidity Factor
Missouri summers combine heat with humidity. An AC that short-cycles (turns on and off quickly) doesn't run long enough to remove adequate moisture from the air. The result is a house that feels cool on the thermostat but clammy and uncomfortable. This can indicate an oversized system — a counterintuitive problem where bigger equipment performs worse on comfort.
We provide home services in St. Peters and throughout the surrounding area. For complete HVAC assessment and repair, visit our heating and cooling services page — we serve St. Charles, St. Louis, Lincoln and Warren Counties.
If your AC is working hard but not delivering, call (636) 397-3200 or schedule service online at aaastl.com. Our technicians do not work on commission and will give you a straight diagnosis of what's actually happening.
