Anytime an air conditioner blows warm air, it can be frustrating. Before calling for help, there are several things you can do to troubleshoot the issue yourself. In many cases, though, you’ll need to contact a professional HVAC company to get a lasting solution.

Check the Thermostat

The first step is to inspect the thermostat settings. It’s possible someone accidentally switched it to "heat" or raised the temperature. It may also be set to "fan only," which circulates air without cooling it. If the display is flickering or blank, try replacing the batteries. Dead batteries or incorrect settings are common and easily fixed causes of warm air.

Swap Out the Air Filter

A dirty air filter can block airflow and reduce your AC's ability to cool effectively. If the filter is completely clogged, it can restrict airflow enough to cause the unit to blow warm air. To prevent this, change your air filter every 60 to 90 days. For ductless systems, filters should be cleaned or replaced every two weeks.

Listen for a Refrigerant Leak

Refrigerant is essential for cooling your home. If there’s a leak, the system cannot cool properly. A hissing or bubbling sound near the refrigerant line may indicate a leak. Since refrigerant is hazardous, only a certified HVAC technician should repair the leak and recharge the system.

Check for Ice on the Refrigerant Line

Ice on the refrigerant line often means restricted airflow or low refrigerant levels. If you see ice, turn off the unit to allow it to thaw. Then, call a professional. The technician may need to check refrigerant levels or look for airflow blockages in the filter or ductwork.

Check Whether the Outdoor Unit Is Running

Your AC system consists of an indoor unit and an outdoor condenser. If the outdoor unit isn’t running, the system cannot cool properly. A silent or non-functioning outdoor unit may point to a tripped breaker, electrical issue, or failed capacitor. These issues require professional repair.

Inspect the Compressor

If the outdoor unit is running but you still have warm air, the compressor may be failing. Warning signs include weak airflow, continuous operation without cooling, or unusual sounds like buzzing or clanking. A faulty compressor should never be repaired by a homeowner due to electrical risks and the potential for further damage.

Make Sure the Breaker Didn’t Trip

Sometimes, warm air is the result of a tripped circuit breaker. If the breaker for the outdoor unit trips, the fan inside may still run, but the compressor will not. Resetting the breaker may restore proper function. If the breaker trips again, call a professional to diagnose the cause.

Inspect the Drain Line for Clogs

The AC’s condensate drain line removes moisture from the system. If it becomes clogged with dirt, algae, or mold, it can trigger a float switch that shuts the system down to prevent water damage. This may result in the AC blowing warm air. Regular maintenance helps prevent clogs and keeps the system running efficiently.

Review Any Error Codes or Lights

Thermostats or AC control boards often display error codes or lights that can help identify problems. A solid red light usually indicates an issue that needs attention, while flashing lights may signal more serious failures, such as electrical faults or communication errors between components. Refer to your system’s manual to decode the alert and guide your next step.

Reset the System

If you’ve checked for all common problems and the AC still isn’t cooling, try a system reset. Turn off the thermostat and switch off the breaker for the AC unit. Wait five minutes to allow the system to reset fully, then restore power and turn the thermostat back on. If the AC still blows warm air, schedule service with a qualified HVAC technician.

Understanding the Importance of Annual AC Maintenance

Routine AC maintenance is essential to keeping your system running efficiently. During a tune-up, we inspect components like refrigerant lines, coils, wiring, and fans. Early detection of issues such as leaks, wiring faults, or airflow restrictions can prevent system breakdowns and restore cooling performance.

We also clean the evaporator and condenser coils, change filters, flush drain lines, and inspect the blower fan. Dirty components reduce cooling capacity and may cause warm air issues. Proper maintenance improves system efficiency and extends equipment life.

Technicians also check refrigerant levels and recalibrate the thermostat to ensure accurate temperature control. This ensures your AC cycles properly and responds to changes in temperature, keeping your home cool all summer.

Call One Hour Heating & Air Conditioning® for Emergency Service

At One Hour Heating & Air Conditioning®, we provide emergency AC repair services to restore comfort quickly. Our licensed technicians use advanced diagnostics to determine why your system is blowing warm air and deliver fast, effective solutions.

We’re available 24/7 to handle any issue, whether it’s a failed compressor, low refrigerant, faulty thermostat, or clogged drain line. We also service ductless units and central cooling systems with professional installation, repairs, and maintenance.

If you’re experiencing cooling problems in Herrin, IL, call One Hour Heating & Air Conditioning® today to schedule service. We’ll make sure your system is running efficiently so you can stay cool and comfortable.