1. Thermostat: COOL mode, batteries, setting
Confirm it's on COOL (not FAN or OFF), set it 5 degrees below the room temperature, and swap the batteries if the screen looks faint or blank. A dead thermostat looks exactly like a dead AC.
2. Breaker panel
Find the breakers labeled AC, air handler, or condenser — there are usually two. If one sits between ON and OFF, flip it fully OFF, then back ON. If it trips again right away, stop — that's a real electrical fault, leave it off and call.
3. The float switch (Miami's classic)
Our humidity clogs AC drain lines with algae constantly. When the drain backs up, a small safety switch cuts the whole system off to prevent a ceiling flood. If your air handler is in a closet or attic, look for water in the drain pan. A clogged drain is a cheap, fast fix — and the number one 'sudden death' cause we see in South Florida.
4. Air filter
A fully choked filter can freeze the coil and shut cooling down. Pull it out and look through it toward a light. If nothing gets through, replace it — but note the system may need hours (fan on, cool off) to thaw before it cools again.
5. The outdoor disconnect
Next to the outdoor unit there's a small gray box. Landscapers and kids have been known to pull the plug inside it. Make sure it's seated.
6. Give it five minutes
ACs have built-in delays that prevent the compressor from restarting instantly. After any change, wait five full minutes before deciding it didn't work.