The system is running but the air coming from the vents is warm or room temperature. Before you call anyone, check one thing that fixes this about a third of the time.
The fan setting
Look at your thermostat. There are two fan settings: "auto" and "on."
Auto means the fan runs only when the compressor is actively cooling. The air coming from the vents is always cold because the fan only pushes air when the coil is cold.
On means the fan runs continuously, even between cooling cycles. When the compressor cycles off — which is normal, it runs in intervals — the fan keeps blowing, but now it is pushing room-temperature air through the ducts. It feels warm because it is. There is nothing wrong with the system.
Switch the fan to "auto." If the air coming from the vents is cold during the cooling cycle and warm between cycles, this was the problem.
If the fan is already on auto
Dirty air filter. A severely restricted filter reduces airflow across the evaporator coil. The coil gets too cold, ice forms, and the system either shuts down on a safety or runs with the coil partially blocked. Either way, the air reaching your rooms is barely cooled. Replace the filter and check the coil for ice (see our post on AC freezing up).
Outdoor unit not running. Go outside. Is the condenser fan spinning? Is the compressor humming? If the outdoor unit is completely silent, the indoor blower will still push air through the ducts, but no heat is being rejected outside. Check the breaker and the disconnect box. If both are on and the outdoor unit is still dead, the contactor, capacitor, or compressor has failed.
Low refrigerant. The system runs but cannot absorb enough heat from the air. The air coming from the vents is cool but not cold — noticeably warmer than normal. The house slowly warms up. A refrigerant leak requires a technician to locate, repair, and recharge.
Dirty condenser coil. If the outdoor unit's aluminum fins are caked with dirt, pollen, or cottonwood, the system cannot reject heat efficiently. Cooling capacity drops. You can gently rinse the fins with a garden hose from the inside out. Do not use a pressure washer — it will flatten the fins and make the problem worse.
When to call
If the fan setting was the issue, you are done. If the air is still warm after checking the filter, confirming the outdoor unit is running, and rinsing the condenser, the problem is likely refrigerant or compressor related.
Call (727) 477-3256 — available 24 hours.