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Why your AC is blowing warm air in Chicago homes (and what to do)
Warm air from the vents on a humid Chicago afternoon is more than uncomfortable. The cause is often simple, and a few quick checks can tell you whether you need a technician.
Quick checks to try first
- Thermostat: set it to Cool, fan on Auto, and a temperature below the room temperature.
- Filter: a clogged filter chokes airflow and can ice up the indoor coil. Replace it if it's dirty.
- Breakers: check the breaker panel and the outdoor disconnect box.
- Outdoor unit: clear leaves and debris from around the condenser and make sure the fan is spinning.
- Ice: if you see ice on the indoor coil or the thick refrigerant line, switch the AC off and run only the fan so it can thaw.
Common causes technicians find
- Low refrigerant. Refrigerant isn't used up, so a low charge means a leak. Topping it off without finding the leak only delays the next failure.
- A failed capacitor or contactor, so the outdoor fan or compressor can't start.
- A dirty condenser coil that can't release heat.
- A frozen evaporator coil from poor airflow or low charge.
- A failing compressor, the most expensive repair on the list.
When to call
If the quick checks don't fix it, shut the system off and call. Running an AC with a frozen coil or a dead outdoor fan can damage the compressor. A technician measures refrigerant pressures, superheat and subcooling and the electrical readings at the outdoor unit to find the real fault instead of guessing.
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