emzone 12a A/C Stop Leak seals leaks permanently in metal and rubber parts, including evaporators, condensers, driers, O-rings, and gasket joints. It also improves system efficiency and prevents future leaks. The emzone 12a A/C Stop Leak is safe for all systems and will not clog or restrict flow. The 114 g can contains sufficient stop leak to stop minor leaks in 2 lb. to 5 lb. A/C systems.