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On the hottest Upstate SC summer days — when temperatures push into the mid-90s along the I-85 corridor from Greenville to Spartanburg — it’s normal for your AC to run for extended periods. Our technician Tim, who handles HVAC calls across Greenville, explains the difference: “On a 96°F day, your system might run 18 out of 24 hours and that’s fine — it’s designed for that. But if it’s running nonstop on an 85°F day in May and can’t hold temperature, something’s wrong.” Here’s how to tell the difference.
Normal vs. Abnormal
Normal: Your AC runs in longer cycles (20-30 minutes) during extreme heat and may run nearly continuously on the hottest days of the year if the outdoor temperature significantly exceeds the system’s design capacity.
Not normal: Your AC runs nonstop but the house never reaches the thermostat setting. The system ran fine last summer but now can’t keep up. The AC runs all day when outdoor temperatures are moderate (80-85°F).
Common Causes
Dirty Air Filter
A clogged filter restricts airflow across the evaporator coil, reducing the system’s cooling capacity. The system runs longer because it’s moving less air. This is the simplest and most common fix – check and replace the filter.
Dirty Condenser Coils
The outdoor unit rejects heat through the condenser coils. When those coils are coated with dirt, grass clippings, pollen, or cottonwood seeds, heat transfer is impaired. The compressor works harder and the system runs longer to achieve the same cooling.
Clean the condenser coils annually with a garden hose (gentle spray from inside out). For heavy buildup, a professional coil cleaning with appropriate chemicals is more effective.
Low Refrigerant
A refrigerant leak reduces the system’s ability to absorb and transfer heat. The AC runs constantly but produces insufficient cooling. You may also notice ice forming on the refrigerant lines or evaporator coil.
This requires a professional leak repair and refrigerant recharge. Simply adding refrigerant without fixing the leak is a temporary (and expensive) band-aid.
Undersized System
If your AC has always struggled to cool the house – especially since you moved in – it may be undersized for the space. This is more common than you’d think. We’ve seen 2-ton systems on 2,000+ square foot homes that need 3.5-4 tons. Additions, sunrooms, and converted garage spaces also increase the load beyond the original system’s capacity.
A proper Manual J load calculation determines what your home actually needs. Upgrading to a correctly sized system eliminates the problem and reduces energy waste.
Duct Leaks
Leaking ductwork in the attic or crawlspace wastes cooled air before it reaches your living spaces. The thermostat never reaches the set temperature because a significant portion of the cooling is escaping. Duct leaks can waste 20-30% of your system’s output.
Aging Equipment
As AC systems age, components wear and efficiency declines. A system that maintained 75°F easily at age 5 may struggle to maintain 78°F at age 15. Compressor efficiency drops, coils degrade, and refrigerant charge may be slightly off. If your system is 12-15+ years old and running constantly, it’s approaching end of life.
Thermostat Issues
A thermostat in direct sunlight, near a heat source (lamp, oven, dryer vent), or on an exterior wall can read higher than actual room temperature, causing the system to run unnecessarily. A poorly calibrated thermostat has the same effect.
The Energy Cost of Constant Running
An AC that runs 20 hours a day instead of 12 is using 67% more electricity. On a 3-ton system drawing 3,500 watts, that’s roughly $8-$12 extra per day – or $250-$360 per month in excess energy costs. The repair or upgrade often pays for itself within one cooling season.
What to Do
1. Replace the air filter 2. Clean the outdoor condenser coils 3. Verify the thermostat is set correctly and located appropriately 4. Check that all supply and return vents are open and unobstructed
If the system still runs constantly after those checks, call for a professional diagnosis. Our technicians measure superheat and subcooling (refrigerant performance), check airflow, and evaluate the system’s capacity against your home’s cooling load.
YOUTUBE EMBED: One Drain – Waldrop Plumbing Air Electric TV Commercial — @YallCallWally
Call Waldrop Plumbing Air Electric at (864) 536-0887.
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