Here's the sentence that reframes this whole topic: an air conditioner never consumes refrigerant. The charge circulates in a sealed loop, the same pounds year after year. So if your AC "needs a top-off" every June, you don't have a thirsty system — you have a leak, and you've been paying rent on it.
How a low charge behaves
Weak cooling that gets worse as the day heats up; ice forming on the copper line or the indoor coil (low pressure makes the coil run below freezing — then the ice itself blocks airflow and things spiral); long run-times and creeping power bills; sometimes an audible hiss or a patch of oily residue at a fitting, since refrigerant carries oil that marks the exit wound.
Where systems actually leak
The usual suspects, roughly in order: the indoor evaporator coil (formicary corrosion eats pinholes in copper — the classic slow leak), service valve cores and caps, brazed joints and flare fittings on line sets, and outdoor coils damaged by weed-trimmer shrapnel or years of corrosion. Each has a different repair cost, which is why "where" matters more than "whether."
How honest leak-finding works
Electronic sniffers trace concentrated refrigerant; nitrogen pressure tests hold the system at pressure and watch the gauge; UV dye catches slow weepers over time; and the frost pattern plus gauge readings narrow the neighborhood before any of that starts. What honest looks like: a found leak, a named location, and a written quote for the actual repair — versus the "add two pounds, see you next year" subscription, which by the third summer has cost more than most repairs.
The legal part
Handling refrigerant — recovering it, repairing the circuit, evacuating and weighing in a fresh charge — is work done under EPA Section 608 rules, and venting it is illegal besides being bad craft. This is the one AC repair category with zero DIY path, and the canned "recharge kits" with sealer are how systems earn their death sentence (sealant gums up valves and contaminates equipment techs then refuse to connect to).
The decision framework
Small leak at a valve core or fitting: fix it, always. Leaking evaporator coil on a system with years left: coil replacement usually pencils. Leaking coil on an aging R-22 system: that's a bigger conversation — we wrote a whole guide on it — and we'll give you the numbers both ways. Either way you'll know where the refrigerant went, which beats wondering every June.