An AC that runs but blows warm or room-temperature air is almost always one of four things. Start with the simplest: a clogged air filter chokes the evaporator, frosts the coil, and drops cooling output. Replace the filter and run the system with the fan off for 30 minutes to let any ice melt.
If that doesn't fix it, the next most common cause in Sacramento is a failed start or run capacitor — the little cylindrical component inside the outdoor unit. When a capacitor fails in the heat, the compressor can't start, the outdoor fan may stop spinning, and indoor air stays warm. This is a $150 to $300 repair and one of the fastest summer calls we handle.
A dirty condenser coil — packed with cottonwood fluff, pet hair, or yard debris — causes the system to trip on high pressure and stop cooling effectively. This is the single most common cause of performance decline during peak summer. A refrigerant leak is the fourth likely cause; a low charge means the system runs but cannot absorb enough heat to deliver cold air at the vent.
If you hear the outdoor unit running but the air at the vent stays warm, shut the system off before something damages the compressor and call for service.