Why is my AC blowing warm air?

Start with the easy checks: is the thermostat actually set to cool and calling for it, and is the outdoor breaker on? If those check out, the culprit is almost always one of four things. A refrigerant leak means the system is low on the chemical that actually moves heat out of your house — it won't just "run low" over time, something is leaking, and refrigerant needs to be found and fixed, not just topped off. A frozen evaporator coil (often from restricted airflow — a dirty filter is the classic cause) blocks heat transfer entirely; if you can see or feel ice on the indoor unit or lines, that's your answer, and running it more just makes the ice worse. A failing compressor is the expensive one — it's the heart of the system, and once it's going, warm air is often the first symptom. And electrical issues, from a bad capacitor to a tripped breaker, can leave the outdoor unit not running at all while the indoor blower keeps circulating room-temperature air, which feels like "warm air" even though nothing's actually broken in the traditional sense.

The honest diagnostic path is pressures and electrical readings, not part-swapping. A tech with gauges on the system in five minutes knows which of these four it is — guessing costs more than diagnosing.