Quick answer
When a Miami AC will not turn on at all, the usual causes are a tripped breaker, a float switch that shut the system off because the drain is clogged, a blank thermostat, a blown low-voltage fuse on the air handler board, a failed transformer, or a disconnect switch left off. Check the thermostat and breakers first, then call for diagnosis.
Written by Sylvia Denton, HVAC Guides Editor. Updated 2026-09-22.
A completely dead system is different from one that runs without cooling. If nothing starts, the problem is almost always in the power or control circuit: something is stopping the signal from the thermostat from reaching the equipment.
In Miami the single most common reason is the float switch. When the condensate drain clogs and water rises in the pan, the switch cuts the low-voltage circuit so the unit cannot overflow. To the homeowner, it looks like the AC just died.
We trace the circuit from the thermostat to the air handler board to the outdoor unit, testing voltage at each step until we find where it stops.
