Before picking up the phone, run through this list. They are in order from most common to least common. Most take under a minute.
1. Thermostat mode and batteries. Is it set to "cool"? Is the set temperature below the current room temperature? If the display is blank, replace the batteries. If someone bumped the mode to "heat," "off," or "fan only," the system will not cool.
2. Fan setting. If the fan is set to "on" instead of "auto," the air from the vents may feel warm between cooling cycles. Switch to "auto." If the air is cold during the cycle and warm between cycles, this was the issue.
3. Circuit breaker. Go to the electrical panel and check the breaker labeled for the AC or air handler. If it has tripped, switch it fully off, then back on. If it trips again immediately, stop — do not force it. Call a technician.
4. Outdoor disconnect. There is a gray box on the wall near the outdoor unit containing a pull-out disconnect. Confirm it is fully seated. It can vibrate loose or be left out after service work.
5. Float switch. If the system stopped and there is water in the drain pan or on the floor near the air handler, the float switch tripped because the drain line is clogged. Clear the drain line and let the float reset.
6. Air filter. Pull the filter and check it. A severely clogged filter can cause the system to freeze, short cycle, or shut down on a safety. Replace it if it is dirty.
7. Closed vents. Walk the house and confirm all supply vents are open and unblocked. Closed vents change system pressure and can cause problems in other rooms.
If you have checked all seven and the system is still not working, the problem is beyond what you can reach from inside the house. Call (727) 477-3256 and tell us what you found. "I checked the breaker and the filter — the breaker is fine and the filter is new, but the outdoor unit is not running" gives us a starting point.