Why Is My AC Running All Day? What's Normal in CA
Current as of September 2026.
The Rancho Cucamonga warehouse had been running its rooftop HVAC unit for 19 straight hours when the compressor gave out on a Thursday afternoon in late July. By Friday morning, with indoor temperatures climbing past 91 degrees and a weekend shift on the schedule, the owner was staring at a $34,000 emergency replacement estimate and zero backup cooling. How long is your AC actually supposed to run? A properly sized commercial unit in peak Inland Empire summer heat should cycle for roughly 15 to 20 minutes and complete two to three cooling cycles per hour.
How Long Should a Commercial AC Run Per Cycle?
The 15-to-20-minute cycle guideline applies to a well-sized, well-maintained system in moderate heat. In Ontario or Fontana in August, with outdoor temperatures above 105 degrees Fahrenheit, extended run times of 30 to 45 minutes per cycle are not unusual and do not automatically signal a problem. What matters is whether the system is actually reaching its set temperature before shutting off. If the compressor runs for an hour, reaches the thermostat setpoint, shuts down, and repeats that pattern, the system is working as designed under heavy load. The problem starts when the system runs without ever reaching setpoint, because that tells you the equipment cannot keep up with the cooling demand.
Runtime expectations also scale with the size and type of equipment.
Is It Normal for a Commercial AC to Run All Day?
In July and August across the Inland Empire, yes, extended daily run times are normal. Sixteen to eighteen hours of compressor runtime per day is not rare for commercial properties in inland Southern California, where overnight temperatures often stay above 80 degrees and buildings retain heat from the day before. The question is not whether the system runs long but whether it runs efficiently during that time, meaning it cycles, reaches temperature, and recovers without the compressor laboring.
Where continuous operation becomes a red flag is when the system shows two specific patterns at the same time: nonstop runtime combined with inadequate cooling. If your thermostat is set to 74 degrees and your space sits at 82 all afternoon, the system is not underperforming because of the heat alone. Dirty coils, a refrigerant leak, a failing compressor, or a unit that was undersized for the space when it was installed are all common causes. That last one, undersizing, is more common in commercial retrofits than owners expect, particularly in older Chino and Corona industrial buildings where tenants added square footage or heat-generating equipment without upgrading the HVAC system to match.
For businesses wondering how their commercial property coverage responds to equipment failures, the answer depends heavily on whether a breakdown was sudden and accidental or the result of long-term wear that was never addressed.
Why Commercial HVAC Problems Hit Harder Than Residential Ones
A homeowner whose AC runs all day in August faces discomfort and a higher electricity bill. A business owner facing the same situation is dealing with a completely different set of risks.
California has workplace heat illness prevention standards that apply indoors when mechanical ventilation is the primary cooling method and indoor temperatures reach 82 degrees Fahrenheit. A commercial HVAC failure during a heat event can trigger a mandatory work stoppage, and a mid-sized Fontana manufacturing facility forced to halt a production line for two days could lose $40,000 to $90,000 in output.
Perishable inventory losses in commercial kitchens can run $8,000 to $25,000 in a single extended outage. Most commercial HVAC manufacturers include language that voids coverage if a unit runs in a state of known malfunction without service documentation.
What Does Nonstop AC Runtime Actually Cost a Business?
The direct costs fall into three categories: utility overruns, accelerated equipment wear, and failure-related losses. A commercial rooftop unit running at full compressor load for 20 hours a day instead of cycling normally can add $600 to $2,400 per month to an electricity bill depending on tonnage and local SCE commercial rates, which rose in the 2025 and 2026 rate cycles. That is money leaving the business before anything breaks.
Accelerated wear is harder to see but more expensive over time. A compressor designed for 15 years of normal cycling may reach end-of-life in seven to nine years under heavy load. When a commercial compressor replacement runs $8,000 to $22,000 and a full rooftop unit replacement runs $18,000 to $65,000 or more, compressing that timeline by six or eight years is a serious financial exposure.
Practical Steps for Inland Empire Owners Before the Next Heat Wave
Documentation is the single most protective habit a commercial property owner can build around HVAC. Every service visit should produce a written record that includes date, technician name, findings, and any deferred items. If a claim ever involves equipment failure, the presence or absence of a service history changes how carriers review the situation.
"After we lost our first rooftop unit, we switched to a service contract with quarterly visits and started logging every single HVAC issue. Two years later when a capacitor failed, we had paperwork showing we'd been on top of maintenance and the equipment breakdown claim went through without a fight."
Red Flags That Warrant a Service Call Today
Warm air from vents while the compressor runs continuously points to a refrigerant or coil problem. Ice on refrigerant lines, even in 100-degree heat, signals restricted airflow or low refrigerant. Grinding, clicking, or squealing from the rooftop unit shortens compressor life with every hour of runtime. Short cycling, where the unit runs three to five minutes before shutting off, is often the most damaging pattern of all.
For equipment breakdown protectionthe qualifying condition is almost always that a failure be sudden and accidental rather than the result of gradual deterioration.
How Smart Businesses Build an HVAC Safety Net
Inland Empire businesses that get through summer heat events with the least disruption tend to share a few habits. They carry service contracts with HVAC vendors who offer priority response. They identify rental cooling sources before they need them. And they know, in calm moments, exactly what a forced closure costs per day.
Common Questions
How often should AC cycle on and off in summer?
A commercial AC in good working order should complete two to three cooling cycles per hour, with each cycle lasting roughly 15 to 20 minutes under normal conditions. In extreme Inland Empire summer heat above 100 degrees Fahrenheit, longer cycles of 30 to 45 minutes are common and not automatically a problem, as long as the system is reaching its setpoint temperature before shutting off.
Is it normal for AC to run all day in summer in California?
In inland Southern California, 16 to 18 hours of daily compressor runtime is not unusual for commercial properties during July and August, especially when overnight temperatures stay above 80 degrees. The concern is not total runtime but whether the system is cycling and reaching temperature, since continuous running without adequate cooling indicates a mechanical or sizing problem.
How many hours a day should AC run in summer for a commercial building?
There is no universal standard, since it depends on building size, occupancy, insulation quality, and outdoor temperature. A better measure is whether the system cycles correctly and maintains setpoint. A commercial unit running 18 hours a day and cycling normally is healthier than one running 12 hours a day without ever shutting off.
How long should AC run per cycle in a commercial space?
Commercial systems usually run 15 to 20 minutes per cycle in moderate conditions, but larger buildings, higher heat loads, and peak summer temperatures push that to 30 to 45 minutes per cycle. Cycles shorter than 10 minutes, called short cycling, are a warning sign and tend to cause more compressor wear than extended runs.
Can running AC nonstop void my commercial equipment warranty?
It depends on what caused the continuous running. If service records show a known issue that was not addressed, such as low refrigerant or dirty coils, and the compressor later fails, most manufacturers and carriers will review whether the failure was a result of that deferred maintenance. Documented service history is your strongest protection against a warranty or claim being denied on those grounds.
Protecting Your Business Property With the Right Coverage
At Farmers Insurance - Young Douglas, the agents who work with Inland Empire commercial clients look at HVAC-related risk as part of a broader conversation about commercial property coverage, equipment breakdown protection, and business income coverage. When a rooftop unit fails in the middle of a heat wave, the financial impact spreads across all three of those categories, and a policy that covers one without the others leaves real gaps. If you haven't reviewed your commercial coverage limits recently, or if your building's use has changed since your policy was written, that conversation is worth having before August puts your equipment to the test. You can review your current coverage options for California businesses or call (909) 303-3722 to speak with a licensed agent directly.
Sources:
- California DIR. "Indoor Heat Illness Prevention Standard (Title 8 Section 3396)." California Department of Industrial Relations, www.dir.ca.gov/title8/3396.html.
- CalMatters. "California's indoor heat rule takes effect protecting millions of workers." calmatters.org/workers/2024/07/california-indoor-heat-rule.
DISCLOSURE: This article may feature independent professionals and businesses for informational purposes. Farmers Insurance - Young Douglas collaborates with some of the professionals mentioned; however, no payment or compensation is provided for inclusion in this content.