Leak Detection Methods

All refrigerant systems lose a small amount of refrigerant through normal permeation of hose materials and shaft seals — typically less than half an ounce per year. A system that requires significant recharge more than once in twelve months has an active leak that must be found and repaired before recharging. Recharging a leaking system without finding the leak is not a repair.

The most sensitive method for finding small leaks. Move the detector probe slowly — approximately one inch per second — around every fitting, connection, and component in the system. The compressor shaft seal. Both service port caps. All hose connections at the condenser, evaporator, and compressor. The probe must move slowly to detect small leaks accurately — moving too fast misses them. Start at the compressor and work systematically around the system. Electronic detectors can be triggered by other refrigerants, cleaning products, and exhaust — verify any hits by cleaning the area and retesting.

UV-compatible dye is injected into the system through the low-side service port in a specified quantity. The dye circulates with the refrigerant. After operating the AC system for 15 to 20 minutes, inspect all components and lines with a UV light and yellow-tinted safety glasses. The dye glows brightly at any leak point. UV dye stays in the system permanently — many vehicles already have factory dye installed. Always check with a UV light first before injecting more dye into an unknown system.

Used to locate leaks in a fully evacuated system or to pressure test a repaired system before recharging. Nitrogen is inert and safe. Pressurize the evacuated system to the manufacturer's specified test pressure and apply soapy water or leak-detecting spray to all joints and connections. Bubbles identify the leak location. Never use compressed air for AC pressure testing — compressed air contains moisture and the combination of air and refrigerant oil can create a combustible mixture.