It's one of the most frustrating things that can happen when the temperature starts climbing: your air conditioner is running, the fan is blowing, but your house just won't cool down. You check the thermostat — it's set correctly. You listen — the outdoor unit is humming. But the air coming out of the vents is barely cool, or not cool at all.
This is the #1 call we get in May and June in Homer Glen and the southwest Chicago suburbs. Here's a systematic breakdown of the most common causes — and what to do about each one.
1. Dirty Air Filter (Check This First)
A clogged air filter is the most common cause of poor AC performance — and the easiest to fix. When the filter is blocked, airflow through the system drops dramatically. The evaporator coil can't absorb heat efficiently, the system works harder, and your home stays warm. Check your filter right now. If it's gray and clogged, replace it. Filters should be replaced every 1–3 months during cooling season.
2. Low Refrigerant (Freon Leak)
Refrigerant is the substance that actually removes heat from your home's air. If your system has a leak, refrigerant levels drop and the AC loses its ability to cool effectively. Signs of low refrigerant include: the system runs constantly but never reaches the set temperature, ice forming on the refrigerant lines or outdoor unit, or a hissing/bubbling sound near the unit. Low refrigerant is not a DIY fix — it requires a licensed HVAC technician to locate the leak, repair it, and recharge the system.
3. Dirty or Frozen Evaporator Coil
The evaporator coil (located in your indoor air handler) is where heat transfer happens. If it's coated in dust and debris, or if it freezes over due to restricted airflow or low refrigerant, it can't do its job. A frozen coil will cause the system to blow warm or room-temperature air. Turn the system off and let it thaw completely (this can take several hours), then check your filter. If it keeps freezing, call for service.
4. Condenser Coil Is Dirty or Blocked
The outdoor unit (condenser) releases the heat that was removed from your home. If the condenser coils are caked with dirt, grass clippings, or cottonwood seeds — very common in Illinois in May and June — the system can't release heat efficiently and cooling capacity drops. You can gently rinse the outdoor unit with a garden hose (with the system off). Make sure there's at least 2 feet of clearance around the unit.
5. Thermostat Problems
Before assuming a mechanical problem, check your thermostat settings. Make sure it's set to COOL (not HEAT or FAN ONLY), the set temperature is below the current room temperature, and the fan is set to AUTO (not ON). If the fan is set to ON, it runs continuously — even when the AC isn't actively cooling — which can make it feel like the system isn't working.
6. Ductwork Leaks
If your ducts have gaps, holes, or disconnected sections, cooled air escapes into your attic, crawl space, or walls before it reaches your living areas. You'll feel air coming from vents, but it won't be as cold as it should be, and some rooms may be noticeably warmer than others. Duct leakage is a common problem in older homes in the southwest Chicago suburbs.
7. AC System Is Undersized for Your Home
If your AC runs constantly but can't keep up on hot days (above 90°F), the system may simply be too small for your home. This is especially common in homes that have had additions built, or where the system was sized incorrectly when installed. On extremely hot days, even a properly sized system may struggle — but if it can't maintain a reasonable temperature on a typical 85°F day, it's worth having a professional evaluate the system sizing.
8. The System Is Too Old
AC systems lose efficiency as they age. A 15-year-old system may be running fine mechanically but simply can't cool as effectively as it once did. If your system is 12+ years old and struggling to keep up, it may be time to consider replacement. A new high-efficiency system can cool your home more effectively while using significantly less electricity.
When To Call a Professional
If you've checked the filter, cleared the area around the outdoor unit, and verified the thermostat settings — and your AC still isn't cooling — it's time to call. Todd's HVAC Services offers same-day AC service throughout Homer Glen, Orland Park, Tinley Park, Mokena, and the southwest Chicago suburbs. We'll diagnose the problem and give you an upfront price before any work begins.
Call or text: 708-742-7935
Related: 7 Signs Your AC Won't Make It Through Summer | AC Repair & Installation — Homer Glen