Your AC is a sealed system. The refrigerant that came in it from the factory should still be in it 20 years later. If yours is low, something is leaking — and just adding more refrigerant every summer is throwing money away (R-410A is around $100–$200 per pound right now, and R-22 is way more).
Most leaks are in three places: the indoor evaporator coil (microscopic 'formicary' corrosion pinholes), the outdoor condenser coil (rust or impact damage), or the lineset/connections (vibration over decades). Finding them takes a real electronic leak detector and sometimes a nitrogen pressure test.
Repair pricing depends on where the leak is and how bad. A bad Schrader valve or fitting is $349. An evaporator coil leak usually means coil replacement ($1,400–$2,800). A condenser coil leak on an older R-22 system often makes more sense to replace the whole system. We'll tell you straight which it is.
What it costs in San Antonio
$349–$2,800+ — Leak detection $189. Repair price depends on location. Some leaks aren't worth fixing — we'll tell you when. Our $59 diagnostic is waived when you approve the repair, so you only pay for the fix itself.