AC Repair: Why Your AC Is Running But Not Cooling (Common Causes & Fixes)
- All Pro
- Oct 17
- 5 min read
Few things are more frustrating than walking into your home or business, feeling warm air blowing from the vents, and realizing your air conditioner is running but not cooling. You can hear the fan spinning and the system humming, but the indoor temperature refuses to drop.
This is one of the most common AC repair issues homeowners and business owners face—especially during peak summer months. The good news is that it’s often caused by fixable problems like dirty filters, low refrigerant, or electrical faults.
In this guide, we’ll break down:
The most likely reasons your AC isn’t cooling,
Safe DIY checks you can perform, and
When to stop troubleshooting and call a professional.
Whether you manage a household or a commercial property, understanding the root causes helps prevent system damage and costly breakdowns.
Table of Contents
Common Causes of an AC Running But Not Cooling
When your air conditioner runs but doesn’t cool properly, the issue could stem from multiple factors—some simple, others more complex. Below are the most common culprits.
1. Dirty or Clogged Air Filter
A clogged air filter restricts airflow, reducing the system’s cooling capacity. When the evaporator coil can’t get enough air, it may freeze, leading to warm air blowing through your vents. Solution: Replace or clean filters every 1–3 months, especially during heavy usage periods.
2. Low Refrigerant Levels (Freon)
Refrigerant is the fluid that absorbs heat inside your home and releases it outdoors. If your AC is low on refrigerant, there’s likely a leak, not just natural depletion. Warning Signs:
Hissing or bubbling sounds near the outdoor unit.
Ice buildup on refrigerant lines or coils.
Extended cooling cycles with little temperature change. Solution: A licensed HVAC technician must locate and repair the leak, then recharge the system.
3. Dirty Condenser Coils
Outdoor condenser coils can become coated with dirt, leaves, or debris, blocking heat transfer. This forces your system to work harder and cool less effectively. Solution: Turn off power and gently rinse coils with a garden hose once or twice a year—or call for professional coil cleaning.
4. Faulty Compressor or Capacitor
If your AC compressor isn’t functioning properly, refrigerant won’t circulate, resulting in warm airflow. Similarly, a faulty capacitor may prevent the compressor from starting at all. Solution: These are electrical components and should only be tested and replaced by a professional HVAC technician.
5. Thermostat Issues
Sometimes the issue isn’t mechanical—it’s your thermostat. Incorrect settings, low batteries, or miscalibration can cause your AC to run without properly cooling. Solution: Ensure the thermostat is set to “cool” and lower than your current room temperature. Replace batteries if needed and check for error codes.
6. Leaky Ductwork
Cracks or holes in ducts can allow cooled air to escape before it reaches your rooms. This problem is especially common in older homes or systems with flexible ducting. Solution: Seal small leaks with mastic sealant or have a professional inspect for larger duct issues.
DIY Troubleshooting Before Calling for AC Repair
Before scheduling an AC service call, you can perform a few safe troubleshooting steps to rule out simple issues.
1. Check the Air Filter
If your air filter looks dirty or clogged, replace it immediately. This is the number one cause of weak airflow and poor cooling performance.
2. Inspect Your Thermostat Settings
Ensure your thermostat is set to “cool” mode and the temperature is several degrees below the room temperature.
3. Examine the Outdoor Unit
Go outside and check if the condenser fan is spinning and if there’s debris around it. Remove leaves, dirt, and other obstructions that can block airflow.
4. Look for Frozen Coils
If you notice frost or ice buildup on refrigerant lines, turn off your system and let it thaw completely. Frozen coils can indicate airflow or refrigerant issues.
5. Check the Circuit Breaker
Sometimes, the indoor or outdoor unit trips a breaker, causing only part of the system to run. Reset tripped breakers and observe if the issue repeats—if it does, call a professional.
6. Listen for Unusual Noises
Grinding, buzzing, or clicking noises can point to electrical or mechanical issues. If you hear them, shut off your system and contact an HVAC technician immediately.
Performing these checks may resolve minor problems, but avoid taking apart electrical or refrigerant components.
When to Call a Professional HVAC Technician
If your AC still isn’t cooling after basic troubleshooting, it’s time to bring in a certified technician. Professional AC repair ensures your system runs safely and efficiently.
Situations That Require Professional Service:
The outdoor unit hums but the fan isn’t spinning.
The system runs continuously but doesn’t reach target temperature.
There’s ice on the refrigerant lines or evaporator coil.
You smell burning or notice smoke from the vents.
You suspect an electrical issue or refrigerant leak.
What the Technician Will Check:
Refrigerant pressure levels and leak detection.
Compressor and capacitor functionality.
Airflow measurements and duct inspections.
Electrical continuity and control board diagnostics.
By scheduling professional AC repair, you prevent further damage, lower utility bills, and extend the lifespan of your HVAC system.
Additional Insights / FAQs
Why is my AC blowing warm air?
Most likely causes are low refrigerant, dirty coils, or restricted airflow from a clogged filter.
Can low refrigerant damage my AC?
Yes—running your system with low refrigerant can overwork the compressor and cause permanent damage.
Is it safe to run my AC if it’s not cooling?
No. Prolonged operation under these conditions can lead to component failure and higher repair costs.
How often should I schedule AC maintenance?
At least once a year—preferably in spring before heavy summer use.
What temperature should my AC blow?
The air from your vents should be 15–20°F cooler than the air entering your return ducts.
The air from your vents should be 15–20°F cooler than the air entering your return ducts.
Conclusion
If your AC is running but not cooling, the issue could be as simple as a dirty filter or as serious as a refrigerant leak or compressor failure. While homeowners can handle minor checks like filter replacement and thermostat calibration, deeper issues demand professional care.
At All Pro Heating, Air & Plumbing, we provide expert AC repair services in Indianapolis, ensuring fast diagnosis, quality repairs, and reliable performance. Whether it’s a minor tune-up or a major component replacement, our certified technicians are ready to restore your comfort.
Don’t let a warm house ruin your day—Contact All Pro Heating, Air & Plumbing for same-day AC repair service in Indianapolis!
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