Quick answer
When a Miami AC runs but does not cool, the usual causes are a failed capacitor on the outdoor unit, a clogged filter or dirty evaporator coil, a refrigerant leak, a frozen coil, or ductwork leaking into a hot attic. A technician measures temperature split, pressures and airflow to find which one it is before replacing anything.
Written by Sylvia Denton, HVAC Guides Editor. Updated 2026-09-22.
A system that runs without cooling is more frustrating than one that is plainly dead, because it looks like it is working. In our service calls across Miami-Dade, the answer is almost never a mystery once the right readings are taken. The job is to measure, not guess, and to avoid the common trap of adding refrigerant to a system that was never low on charge.
The first number we take is the temperature split: the difference between air entering the return and air leaving the supply. A healthy system in Miami humidity usually shows 16 to 21 degrees. A split under 12 points toward charge, airflow or the compressor. A normal split with a warm house points toward the house itself, meaning duct leakage, an undersized system or an attic with no insulation over the living room.
From there it is pressures, superheat and subcooling on the refrigerant side, static pressure and filter condition on the air side, and a look at the condenser coil, which in Miami can be packed with cottonwood fluff, grass clippings and salt film by midsummer.
