In a perfect world your A/C unit should not lose any refrigerant. Unfortunately, leaks do occur and sometimes they are almost impossible to find. The problem could be in the evaporator coil, the line set, or the condenser.
Typically leaks are found around brazing joints, fittings, or service valves. Refrigerants are in an oil base so any oily areas are indicative of a leak. Those are the easy ones to fix. The difficult ones are usually in the evaporator coil or condenser. A common problem with older systems is when dogs urinate on the condenser fins. The urine is highly corrosive and will erode the aluminum condenser fins and tubing which will cause refrigerant leaks.
The methods for finding refrigerant leaks are:
- Visual — Look for oily residue
- Audible — Listen for a hissing sound
- Soap Bubbles — Shows if a leak is present
- Electronic — Instruments that emit an audible sound when detecting refrigerant
- Dye — Coloring agent injected into system then use a UV light to see signs of the dye on the problem area
- Pressure Check — Use nitrogen to pressure check the condenser and then the evaporator coil, this usually finds the problem