The call came in [UPDATE: time of day and approximate date, e.g. "at 8am on a Tuesday in late June"]. A WaterColor vacation rental, guests in the property, thermostat reading 81°F with the AC running. The property manager needed a tech on-site before checkout at 10am.
We were there by [UPDATE: time, e.g. "9:15am"].
What the diagnostic found
The outdoor unit was running. The indoor air handler was running. Airflow at the supply registers was normal. Suction line at the outdoor unit was warm — not cold, which it should be when refrigerant is boiling correctly in the evaporator coil. Refrigerant charge was down by approximately [UPDATE: how many pounds low, e.g. "two and a half pounds"] on a system spec'd to hold [UPDATE: total system charge, e.g. "eight pounds"].
A system doesn't lose refrigerant through normal operation. Refrigerant is a closed loop. What it loses through is a leak — usually at a fitting, a coil joint, or a corroded line-set connection. We traced it to [UPDATE: where the leak was, e.g. "a pinhole at the evaporator coil header, likely accelerated by coastal salt-air exposure at the coil face"].
The system was [UPDATE: age, e.g. "nine years old"]. On a system that age in good condition otherwise, evaporator coil replacement makes sense. On a system much older, the math tilts toward full replacement. This one was repairable.
The repair
We recovered the remaining refrigerant, replaced the evaporator coil with a [UPDATE: coil make/model, e.g. "TXV-equipped replacement coil matched to the existing air handler"], pressure-tested the system to [UPDATE: test pressure, e.g. "410 PSI with nitrogen"] for [UPDATE: hold time, e.g. "30 minutes with no drop"], pulled vacuum, and recharged to manufacturer-spec. Total time on-site: [UPDATE: hours, e.g. "four and a half hours"].
Guests were able to stay. The system reached setpoint within [UPDATE: e.g. "40 minutes"] of recharge. Checkout proceeded normally.
The property manager was on-site for walkthrough at [UPDATE: time] and confirmed everything was operating before the next guests arrived.
Refrigerant leaks don't announce themselves until the system can't keep up. If your 30A rental's energy bills have crept up over the past two or three summers without explanation, a refrigerant charge check during a maintenance visit is a reasonable first look. Maintenance plans here.