HVAC in Charleston spends its life removing humidity, then loses a cabinet to salt. Condensers on the peninsula, the islands, and Mount Pleasant crust at the fins, the contactor, and the disconnect. The cooling season is long. The heating season is a brief inconvenience, not the reason the equipment was bought. Attic and closet air handlers still overflow a clogged condensate line and stain a ceiling so the drip gets blamed on the roof. Summerville is a little less salty and just as humid. Say which air your outdoor unit breathes.
When the cooling quits, note if that outdoor unit is silent, cycling too fast, or sweating ice on the line. A filter packed with pollen and a weak return can mimic a dead compressor. Ask what is ruled out before a major part is condemned. Heat failures happen, usually on the one cold week. Say if you smell combustion. Do not treat a space heater as the repair. In a flood-prone ground level, say whether the equipment itself sat in water. That is a different verdict from a dirty filter.
Replacement should be sized for this house and this moisture, not copied from the faded nameplate. Ask about ducts in a tight historic house, where they may be undersized or missing on the upper floor. Indoor and outdoor pieces should be a matched pair. A new condenser on a tired coil needs a plain explanation. Humidity is the test. Cold clammy air in August is a failure even if the thermostat number dropped. Ask how the cabinet and the fasteners will live in salt, not in a showroom.
The drain, the float switch, and the pan decide whether the system wets the house it is supposed to dry. Bath fans that stop in the attic make that job harder. On a raised house, the air handler may sit where storm water can reach it. Say so. Maintenance should leave a list of what was cleaned, especially the condensate path and the outdoor electrical connections that salt turns white. A crusted disconnect is not a cosmetic issue.
Say cooling or heat, dead or weak, and say where in Charleston the house sits. HVAC here is a humidity machine living in salt air. Call the number on this page.