Many times you notice your AC runs continuously yet never cools because low refrigerant, blocked airflow from dirty filters or coils, a failing compressor, or improper sizing reduce output; Houston heat and humidity worsen the effect, increasing energy bills and the risk of compressor failure. Have a licensed HVAC technician inspect refrigerant, airflow, and system sizing to restore comfort and efficiency.
Key Takeaways:
- Low refrigerant charge or compressor failure prevents the system from producing cold air even though it runs-have a licensed HVAC technician check for leaks and repair the compressor as needed.
- Restricted airflow from clogged air filters, blocked vents, or dirty evaporator/condenser coils reduces heat transfer so the unit runs continuously without cooling effectively.
- Leaky ducts, poor insulation, incorrect thermostat settings, or extreme Houston heat and humidity can overwhelm an undersized or poorly maintained system-seal ducts, verify settings, and evaluate system capacity.
Common Reasons for AC Running Constantly
Your unit can run nonstop for several technical reasons: dirty filters and coils reduce airflow, an undersized or failing compressor can’t meet cooling load, and poor duct sealing leaks cooled air back into the attic. Thermostat placement and sensor errors also force continuous cycles. In Houston’s heat and humidity, dirty coils and restricted airflow commonly cut capacity by 10-30%, making the system run longer and raising energy bills.
Thermostat Malfunctions
Thermostat errors often mimic mechanical failure: miscalibration, a bad temperature sensor, or improper placement in direct sunlight can keep your AC running. You should check batteries and settings first; many thermostats last 1-2 years on batteries. If the display or wiring looks damaged, replace or have an HVAC pro recalibrate-a bad sensor or loose wire can prevent the system from ever reaching setpoint.
Low Refrigerant Levels
When refrigerant is low from a leak, your AC loses cooling capacity and may run continuously while struggling to hit the thermostat setpoint. Typical signs include reduced airflow, a hissing sound, and ice buildup on the evaporator coil. Modern systems use R‑410A (R‑22 production ended in 2020); handling and recharge must be done by an EPA-certified technician.
Technicians diagnose low refrigerant by measuring pressures and performing superheat/subcooling tests against the manufacturer’s specs, then locating leaks with electronic detectors or UV dye. After repairing the leak, they pull a deep vacuum (to remove moisture), pressure-test, and recharge to the specified pounds/ounces for your 2-5 ton system. Prompt repair prevents compressor burnout and restores designed efficiency.
Impact of Houston's Humidity on AC Performance
Houston’s summer air often has relative humidity above 70%, with dew points in the mid-70s°F, so your AC spends much of its energy removing moisture rather than lowering air temperature. That latent load forces longer runtimes, raises electrical bills, and can make rooms feel clammy at set temperatures that should be comfortable. You may need a system designed for high latent loads to restore the cooling you expect.
Increased Load on AC Systems
When humidity is high, a larger share of your system’s capacity goes to condensation on the evaporator coil instead of sensible cooling. For example, on humid Houston afternoons your AC can run 20-30% longer than on dry days, increasing wear and utility costs. You should check airflow, refrigerant charge, and system sizing if runtimes spike consistently during humid weather.
Importance of Dehumidification
Controlling indoor moisture is imperative because temperatures alone don’t determine comfort; ASHRAE recommends target indoor RH of 40-60%. If your home stays above 60% RH you risk mold growth, musty odors, and persistent discomfort even when the thermostat reads the setpoint. You should evaluate whether your AC can remove enough latent load or if supplemental dehumidification is needed.
Dedicated solutions-like a whole-house dehumidifier or a variable-speed HVAC that maintains longer, gentler runtimes-usually outperform short-cycling systems. In practice, adding a quality whole-home dehumidifier can keep RH near 45-50% during peak Houston humidity, while correcting low airflow and refrigerant issues can restore normal moisture removal. Have a contractor perform on-site humidity measurements and removal-rate estimates before you invest.
System Malfunctions and Faulty Components
When parts wear out, your system can run constantly without cooling effectively: failed capacitors, stuck relays, bad thermostats, or a dying compressor all mimic a “running but not cooling” symptom. In Houston’s 90°F+ summers the extra load accelerates failures, and a bad control board or sensor can keep the blower on while the refrigeration cycle never engages. Watch for cycling patterns and any electrical tripping or burning smells, which indicate immediate service is needed.
Compressor Issues
The compressor is the refrigeration heart; if it’s weak or seized your AC will run but not remove heat. You might hear humming, frequent breaker trips, or long runtimes with little temperature drop. Failed start capacitors or burned windings are common causes, and compressor replacement typically runs $1,200-$3,500 depending on tonnage and labor. Because of the electrical hazard, you should avoid DIY diagnostics beyond noting symptoms and calling a technician.
Clogged Air Filters
Dirty filters restrict airflow, forcing the system to run longer while reducing coil heat exchange and efficiency; a clogged filter can raise energy use by roughly 5-15% and drop the normal evaporator delta-T (15°F) by several degrees. You should inspect filters monthly during heavy-use months in Houston and swap pleated or higher-MERV media every 1-3 months, more often with pets or construction dust.
In practice, a heavily loaded filter can cut airflow by over 20%, causing the evaporator coil to get too cold and sometimes freeze within hours, which further prevents cooling. If you notice weak vents or one room much warmer, change the filter and recheck the supply temperature split; households with dogs, children, or nearby roadwork often need monthly changes to prevent repeated service calls and reduced compressor life.
Ductwork Problems
Duct leaks, blockages, and thin insulation often explain why your AC runs nonstop without getting cool. Leaky runs can dump up to 30% of conditioned air into attics or crawlspaces, blockages raise airflow resistance and shorten compressor life, and uninsulated ducts subjected to 120°F+ attic heat dramatically increase heat gain-forcing longer runtimes and higher bills.
Leaks and Blockages
When ducts leak or get blocked, you’ll notice uneven cooling, dusty vents, and higher energy bills. A single major leak can cost you up to 30% efficiency; technicians use smoke tests or a duct blaster to find losses. Seal seams with mastic or UL 181-rated tape, clear crushed flex runs, and keep returns unobstructed to restore proper airflow.
Insufficient Insulation
Poorly insulated ducts in Houston’s hot-humid climate let heat and moisture into supply lines, forcing your system to run longer and fight humidity. Target an insulation level of R-6 to R-8 for attic or crawlspace ducts; exposed fiberglass or missing vapor barriers can increase indoor humidity and coil freeze/thaw cycles.
Inspect all joints, boots and flex runs for missing wrap or crushed insulation; pay attention to >90° elbows and plenum transitions where heat gain is worst. Apply foil-faced R-6 wraps or add 1 in. closed-cell spray foam (≈R-6) at exposed sections, and repair torn vapor barriers-these steps often cut attic heat gain enough to lower runtimes and humidity quickly.
When to Call a Professional
If your AC runs continuously for more than 30 minutes without reaching the setpoint, if rooms remain >5-10°F warmer than the thermostat, or if bills jump by 20-30%, call a pro; persistent running often signals failing compressor, low refrigerant, or airflow blockages. You can read deeper troubleshooting at Why Is My AC Running, But Not Cooling? and have the information ready when you schedule a technician.
Signs of Major Issues
If you spot ice on the evaporator coil, hear constant hissing or bubbling (possible refrigerant leak), smell burnt wiring, or see frequent circuit trips, those are major warning signs. Measure the temperature split: a healthy system yields about 15-20°F between return and supply; under 10-12°F indicates serious problems that require immediate professional diagnosis to avoid compressor damage.
Choosing the Right HVAC Technician
Ask for technicians with NATE certification, EPA 608 for refrigerant work, proof of insurance, and at least 3-5 years of local experience; demand a written estimate, itemized repairs, and a clear warranty on parts and labor before they start.
Request references from recent Houston jobs, verify online reviews and BBB ratings, and compare at least two written bids. Expect a typical service call fee of $75-$200, refrigerant recharges around $150-$400, and major compressor replacements from $1,200-$3,500; choosing a technician who offers emergency availability (24-48 hours) and a minimum 1-year labor warranty often saves you money and downtime.
Conclusion
When your AC keeps running but never cools in Houston, it is rarely a thermostat issue alone. The most common causes are low refrigerant from leaks, dirty filters or coils restricting airflow, duct losses, failing compressors, or a system that is undersized for Houston’s extreme heat and humidity. These problems force longer runtimes, spike energy bills, and increase the risk of major component failure if they are ignored. While basic steps like changing filters and clearing vents help, persistent issues require professional diagnostics to restore proper cooling and efficiency.
If your home stays warm, humidity remains high, or your system runs nonstop, Global Air Service is here to help. Our licensed Houston HVAC technicians specialize in diagnosing airflow problems, refrigerant issues, duct leaks, and system sizing challenges common in the local climate. We provide clear explanations, honest recommendations, and reliable repairs to get your AC cooling efficiently again. Contact Global Air Service today to schedule expert air conditioning service and protect your comfort before minor issues turn into costly breakdowns.
