AC Blowing Warm Air

A clogged filter restricts airflow across the evaporator coil. The coil can't absorb heat properly, and over time it may freeze solid, blocking airflow entirely.

Pull the filter and hold it up to a light. If light barely passes through, or the filter is gray and dust-caked, it's overdue. Filters should be changed every 1-3 months in cooling season.

Ice has built up on the indoor coil. The unit blows warm air because no heat exchange is happening. Usually caused by restricted airflow OR low refrigerant.

Turn off the AC at the thermostat but leave the blower fan ON for 1-2 hours. Open the air handler panel — if you see ice or water dripping, you found it. Common signs: water around the indoor unit, ice on the copper suction line outside.

The system has lost refrigerant through a leak. Without enough refrigerant, the unit can't move heat efficiently. Refrigerant does NOT get "used up" — if you're low, you have a leak somewhere.

Listen for hissing or bubbling near the copper lines or indoor coil. Look for oily residue around fittings (refrigerant carries oil). Check for ice on the suction line. A pro will use electronic leak detection or UV dye.

The dual run capacitor that starts your outdoor compressor and fan has degraded or failed. If only the fan cap side failed, the compressor may still run but inefficiently.

Look at the outdoor unit: a humming sound but no fan spin is the classic sign. If you can safely access the electrical box (power OFF and discharged), look for a bulging top or oily residue on the capacitor. Test with a multimeter capacitance setting — readings more than 6% below the labeled MFD rating mean replace.

The outdoor condenser unit is off entirely while the indoor blower runs. Common causes: tripped breaker, blown fuse, failed contactor, or thermostat wiring issue.

Walk outside while the AC is supposedly running. Listen for the fan and look at the spinning blades. If silent: check the disconnect box on the wall next to the unit, check your breaker panel, check the inline fuses (some units have small fuses in the disconnect).

The outdoor unit's coils are clogged with cottonwood, grass clippings, or dirt. The system can't reject heat to outside air, so it can't cool indoor air effectively. Severe cases overheat the compressor.

Look at the fins on the outdoor unit. Should be visible metal louvers. If they're packed with debris or matted with cottonwood fluff, that's the problem. Run your hand over them lightly — heavy dust transfers immediately.

Sometimes the simplest cause. Thermostat is in HEAT mode, FAN is set to ON instead of AUTO (constant air movement masks cooling), batteries are dead, or the unit itself failed.

Check thermostat mode (COOL not HEAT/FAN), fan setting (AUTO not ON), and temperature setpoint (5-10°F below room temp). Look for low-battery warnings. If it shows a setpoint but the system never responds, the thermostat may have failed.