Why Is My AC Running But Not Cooling? 7 Common Causes

There is a specific kind of frustration that sets in when you hear your air conditioner humming, but the temperature in your home keeps climbing. It’s an Aurora summer, the humidity is spiking, and while your vents are blowing air, it feels more like a hairdryer than an AC.

When your AC runs but doesn’t cool, it’s often a sign that the system is working hard but failing at the “heat exchange” process. At Artlip and Sons HVAC Solutions, we’ve been diagnosing these cooling mysteries for local homeowners since 1969.

Before you panic, here is a breakdown of why your system might be underperforming and what you can do about it.

1. The “Simple” Checks: Thermostats and Filters

Before diving into mechanical failures, check the basics.

• The Thermostat: Ensure it is set to “Cool” and the fan is set to “Auto.” If the fan is set to “On,” it will blow air constantly—even when the cooling cycle is off—making it feel like the system isn’t working.
• The Air Filter: This is the most common culprit. A heavily clogged filter chokes off airflow. If air can’t pass through the cooling coils, the system can’t remove heat from your home. If your filter looks like a dryer lint trap, replace it immediately.

2. Dirty Outdoor Condenser Coils

Your outdoor unit’s job is to release the heat collected from inside your home. In Illinois, cottonwood seeds, grass clippings, and dirt can quickly coat those outdoor coils. When the coils are buried in debris, the heat stays trapped in your system, and the air coming out of your vents stays warm.

3. A Tripped Breaker

Your AC system actually has two main parts: the indoor air handler and the outdoor condenser. Sometimes, the breaker for the outdoor unit trips, while the indoor unit keeps running. You’ll hear the fan inside, but because the outdoor compressor isn’t running, no “cooling” is actually happening.

4. Frozen Evaporator Coils

It sounds counterintuitive, but your AC can actually freeze solid in the middle of a heatwave. If airflow is restricted (due to that dirty filter we mentioned) or if refrigerant is low, the indoor coils can drop below freezing. If you see ice on the copper lines or the indoor unit, turn the system off and call a professional to let it thaw safely.

5. Low Refrigerant Levels

Refrigerant is the “blood” of your AC. It doesn’t get “used up” like gas in a car; it circulates in a closed loop. If you are low on refrigerant, you have a leak. Signs include a bubbling or hissing sound and air that is lukewarm at best.

6. A Faulty Capacitor or Contactor

Think of the capacitor as a big battery that gives your compressor the “jolt” it needs to start. In Aurora’s summer heat, these components can wear out or blow. If the fan is spinning but you don’t hear the deep rumble of the compressor, this is likely the issue.

7. Ductwork Leaks

Sometimes the AC is cooling perfectly, but the cold air is leaking into your attic or crawlspace before it ever reaches your living room. Torn or disconnected ducts can result in a system that runs non-stop with very little reward.

When to Call the Pros

While a filter change is a great DIY start, most cooling issues involve high-voltage electricity or pressurized refrigerant—both of which require professional expertise.

At Artlip and Sons, we’ve spent over 55 years keeping Aurora comfortable. If your AC is running but the house is still hot, don’t wait for the system to break down entirely. Ignoring a struggling AC can lead to a burnt-out compressor, which is a much costlier fix.

Is your home heating up? Contact Artlip and Sons HVAC Solutions today for an expert diagnostic. We’ll get your cool air back on track.