How to Fix an AC That’s Running But Not Cooling: Common Culprits

There’s nothing more frustrating than turning on your air conditioner, hearing it hum along just fine—yet still sweating because the air coming out is anything but cool. If your AC is running but not cooling, you’re not alone. This is one of the most common HVAC issues homeowners face, especially during those peak summer months when your AC is working overtime.

Fortunately, there are several common causes for this issue—and many of them are simple enough to troubleshoot on your own. Let’s break it down.

1. Incorrect Thermostat Settings

Let’s start with the easiest fix: your thermostat. It might sound obvious, but it’s often overlooked.

What to check:

• Set to “Cool”: Make sure your thermostat is set to “cool” and not just “fan.”
• Temperature setting: Your AC won’t kick on if the temperature on your thermostat is set higher than the current room temperature.
• Dead batteries: If your thermostat is battery-operated, weak batteries can prevent it from working properly.

How to fix it:

Set the thermostat to a few degrees lower than the current temperature. Wait a few minutes to see if you notice cooler air coming out. Replace the batteries if needed.

2. Clogged or Dirty Air Filter

Air filters play a critical role in keeping your AC running efficiently. If they’re clogged with dirt, dust, and debris, airflow is restricted—and that means less cool air gets to you.

Signs of a dirty filter:

• Weak airflow from vents
• Dust buildup around vents
• Musty smell from the AC

How to fix it:

Replace the air filter (most need changing every 1–3 months). You’ll be amazed at the difference a clean filter can make in airflow and cooling performance.

3. Frozen Evaporator Coil

The evaporator coil absorbs heat from inside your home. But when airflow is restricted—often due to a dirty filter or blocked vents—the coil can get too cold and freeze over.

Signs of a frozen coil:

• Ice on the indoor unit or refrigerant line
• Warm air from vents
• Condensation or water pooling around the unit

How to fix it:

• Turn off the AC to let the ice melt. This may take several hours.
• Replace or clean the air filter.
• Make sure all air vents are open and unblocked. If it freezes up again, call a professional—it could be a refrigerant or airflow issue.

4. Refrigerant Leak

Refrigerant is the lifeblood of your AC system. It absorbs heat from inside and releases it outside. If there’s a leak, the system can’t cool properly.

Signs of low refrigerant:

• AC runs continuously but doesn’t cool
• Hissing or bubbling noises
• Ice buildup on refrigerant lines
• Higher energy bills

How to fix it:

This isn’t a DIY fix. You’ll need an HVAC technician to locate the leak, repair it, and recharge the refrigerant. Don’t just “top it off” without finding the leak—it will keep happening.

5. Dirty or Blocked Condenser Unit (Outdoor Unit)

Your outdoor unit plays a major role in releasing heat from inside your home. If it’s covered in dirt, leaves, or grass clippings, heat can’t escape efficiently—which means your AC can’t cool properly.

How to fix it:

• Turn off power to the unit.
• Use a garden hose to gently rinse the condenser coils.
• Remove any debris, leaves, or vegetation around the unit (keep at least 2 feet of clearance). Avoid using high-pressure water or bending the fins.

6. Faulty Compressor

The compressor is the heart of your AC system. If it’s not working right, your system won’t be able to circulate refrigerant or cool your home.

Signs of a failing compressor:

• AC turns on but doesn’t cool
• Clicking or rattling noises from the outdoor unit
• Tripped circuit breaker

How to fix it:

This is another job for the pros. Compressor issues are complex and expensive to repair, so it’s best to have a technician evaluate the problem. In some cases, replacing the unit might be more cost-effective than replacing just the compressor.

7. Electrical Issues

Faulty wiring, a tripped breaker, or a blown fuse can disrupt your AC’s ability to function properly—especially the cooling cycle.

How to fix it:

• Check your breaker box. If the AC breaker has tripped, reset it.
• If it keeps tripping, don’t keep resetting it—call a professional to inspect the system.
• Check for any damaged or frayed wires (only if you’re comfortable doing so safely).

8. Ductwork Problems

Even if your AC is working fine, air may not be reaching your rooms if the ductwork is leaking or blocked.

Signs of duct issues:

• Some rooms are much warmer than others
• Whistling sounds from the vents
• Higher energy bills without improved comfort

How to fix it:

• Inspect visible ducts for signs of damage or disconnection.
• Seal small gaps with foil tape (not duct tape).
• For bigger problems or ducts behind walls, call in a professional.

When to Call a Professional

While many of these issues can be resolved with a bit of DIY effort, there are times when calling an HVAC technician is the smartest move. If you’ve tried the above steps and your AC is still running but not cooling, it’s likely a deeper mechanical or electrical issue that could even require an Air Conditioner Replacement Cincinnati specialist.

Look for a technician who is licensed, experienced, and willing to explain what went wrong—and how they’ll fix it. A people-first technician won’t just treat the symptoms; they’ll find the root cause.

Final Thoughts

When your AC is running but not cooling, it’s easy to assume the worst—but the problem might be as simple as a dirty filter or a tripped breaker. Start with the basic checks, and don’t be afraid to call in help when things go beyond your comfort zone. After all, your comfort (and sanity) matter, especially when the heat’s cranking up.

Stay cool, stay informed—and remember, regular maintenance goes a long way in preventing these issues from cropping up in the first place.