AC Running But Not Cooling? 8 Causes & Fixes (New Lenox, IL)

It's May in New Lenox and the temperatures are climbing. You turn on the AC — it runs, the fan blows, but the house just won't cool down. This is one of the most common calls we get every spring and summer. Here are the 8 most likely causes, starting with the ones you can check yourself right now.

Check These Yourself First

1. Dirty or Clogged Air Filter

This is the #1 cause of AC problems in Will County homes. A clogged filter blocks airflow so severely that the system can't move enough air to cool the space. Check your filter right now — if it's gray or brown, replace it. 1-inch filters should be replaced every 1–3 months during cooling season.

2. Thermostat Set Incorrectly

Make sure the thermostat is set to "Cool" (not "Fan" or "Heat") and that the temperature setpoint is lower than the current room temperature. Also check that the fan setting is on "Auto" — if it's on "On," the fan runs continuously even when the system isn't actively cooling, which can feel like warm air.

3. Tripped Circuit Breaker

Your AC has two circuits — one for the indoor air handler and one for the outdoor condenser. If the outdoor unit's breaker tripped, the indoor fan will run but no cooling happens. Check your electrical panel and reset any tripped breakers. If it trips again immediately, call a professional — there's an underlying electrical problem.

4. Blocked Outdoor Condenser Unit

The outdoor unit needs clear airflow to reject heat. If it's surrounded by overgrown bushes, covered in cottonwood fluff, or has debris inside the cabinet, it can't work efficiently. Clear at least 2 feet of space around the unit and gently rinse the coils with a garden hose.

Problems That Require a Professional

5. Low Refrigerant / Refrigerant Leak

Refrigerant is the substance that actually transfers heat out of your home. If your system is low on refrigerant, it can't cool effectively. Low refrigerant always means a leak — refrigerant doesn't "run out" like gas. An EPA-certified technician must locate the leak, repair it, and recharge the system. This is not a DIY repair.

6. Frozen Evaporator Coil

If you see ice on the indoor unit or the refrigerant lines, the evaporator coil is frozen. This usually happens due to restricted airflow (dirty filter) or low refrigerant. Turn the system off and let it thaw for 2–3 hours, then replace the filter and restart. If it freezes again, call for service.

7. Failing Capacitor

Capacitors are small cylindrical components that start and run the compressor and fan motors. They're the most common electrical failure in AC systems — especially in systems over 5 years old. A bad capacitor causes the compressor or fan to struggle or not start at all. Replacement is a quick repair for a technician.

8. Dirty Evaporator or Condenser Coils

Over years of operation, both the indoor evaporator coil and outdoor condenser coil accumulate dirt and grime that insulates them and reduces heat transfer. A professional coil cleaning restores efficiency and cooling capacity.

When to Call New Lenox Heating

If you've replaced the filter, checked the thermostat, reset the breaker, and cleared the outdoor unit — and the AC still isn't cooling — it's time to call a pro. New Lenox Heating offers same-day AC diagnosis throughout New Lenox, Frankfort, Mokena, Lockport, and all of Will County. Call 815-893-3642. We provide upfront pricing before any work begins.