Check These Two Things Before Calling
Before scheduling a service call, verify these:
1. Thermostat mode: Check that it's set to COOL, not HEAT and not FAN ONLY. Fan-only mode circulates room-temperature air — it feels like warm air even though the system is 'running.' This is the most common call we take that doesn't require a technician.
2. Circuit breakers: Your central AC has two breakers — one for the air handler (indoor unit) and one for the condenser (outdoor unit). If only the outdoor unit breaker has tripped, the fan will blow air but the compressor won't run and you'll get warm air. Check the panel, reset any tripped breaker once. If it trips again immediately, call a technician — something is drawing excess current.
Dirty or Clogged Air Filter
A severely dirty filter restricts airflow to the evaporator coil. When airflow drops too low, the coil temperature drops below freezing and moisture in the air freezes onto it — blocking airflow further in a cycle that ends with a frozen coil and warm air from vents.
Check your filter. If it's visibly gray and clogged, replace it. Turn the system to FAN ONLY for 2–3 hours to allow the coil to thaw completely. Then switch back to cooling. If the system cools normally, a dirty filter was the culprit. Set a reminder to check filters every 30 days.
Low Refrigerant (Most Likely Cause in Older Systems)
Refrigerant is the medium that carries heat from inside your home to the outside. When refrigerant is low, the system can't transfer heat effectively — resulting in warm or only slightly cool air from the vents.
Refrigerant doesn't deplete naturally. Low refrigerant always means a leak — either a slow leak that's developed over years (typically at brazed joints or service valve packing) or a sudden failure.
Signs: warm air, ice on refrigerant lines or the outdoor unit, hissing or bubbling sounds. Fix: a technician locates and repairs the leak, then recharges to the manufacturer's specified level. Simply topping off without fixing the leak is a temporary measure.
Failed Capacitor
Capacitors are cylindrical components that store and release electrical charge to start and run the compressor and fan motors. They're wear items — most fail between 5 and 10 years.
A failed run capacitor means the compressor motor can't start properly or runs at reduced efficiency, producing little to no cooling. You might hear a humming sound from the outdoor unit as the motor tries to start and fails.
Capacitor replacement is one of the cheaper AC repairs: $150–$250 including labor. It's also one of the most common warm-air causes we see in Orange County, especially after a first hot stretch in May.
Dirty Condenser Coil
The outdoor condenser unit rejects heat from the refrigerant to the outside air. When the coil fins are coated with dirt, cottonwood fluff, grass clippings, or debris, heat can't transfer out efficiently. The refrigerant stays too warm and arrives at the indoor coil without enough capacity to absorb heat from your home.
You can rinse the condenser fins gently with a garden hose (outside-in, low pressure) to remove loose debris. For a thorough cleaning, a technician uses coil cleaner and proper rinsing to restore fin efficiency without bending the fins.
Frozen Evaporator Coil
The evaporator coil (indoor unit) can freeze from two causes: restricted airflow (dirty filter, closed vents, duct blockage) or low refrigerant. When frozen, the ice acts as insulation — the refrigerant circulates but can't absorb heat, and warm air passes over the ice block and through the vents.
Fix: Turn the system off (leave the fan running) for 2–4 hours to fully thaw. Then address the root cause — clean the filter, open closed vents, or call for a refrigerant check. Never let a frozen coil defrost without finding the cause, or it will freeze again.
Compressor Failure
The compressor is the heart of the refrigeration cycle — it pressurizes the refrigerant. A failed compressor means no refrigeration, period. The fan will still blow air, but it won't be cooled.
Signs: outdoor unit starts and hums but immediately shuts off, loud clunking or grinding from outdoor unit, or the outdoor unit doesn't start at all while the indoor air handler runs.
Compressor replacement is expensive ($1,200–$2,500) and often tips older systems into replacement territory. If your system is over 10 years old and the compressor has failed, get a replacement quote before committing to the repair.