A/C Leak Test

Common methods are UV dye with a lamp, an electronic leak detector, a vacuum hold test and pressure testing with forming gas. Typical leak points are the condenser, hose connections, O-rings, the compressor shaft seal and the evaporator. Evaporator leaks are hard to see because the part is hidden in the dashboard.

UV dye mixes with the oil in the system and glows at the leak under a UV lamp; electronic detectors react to refrigerant in the air.

A slow loss of cooling over months often points to a small leak rather than a defective component. Oily residue at a joint is a visible hint, because compressor oil escapes together with the refrigerant.