DO NOT USE IN AMMONIA SYSTEMS! Do NOT use this item in a R410a system. You MUST use the Enviro-Safe Proseal XL4 Direct Inject line of products. Metal sealer for leaks in a/c condensers, evaporators, line sets, schrader valves, o rings and solder joints. Proseal XL4 is used in home, heat pump, large automotive and industrial applications. One can will normally repair a leak in systems up from 1.5 to 5 ton. If you have a smaller unit, please contact us. If the a/c system that will not hold a vacuum, you need to use the Enviro-Safe Prodry XL4. The reason for the vacuum or the use of Enviro-Safe Prodry XL4 is that it will eliminate moisture in the system. Moisture mixing with oils and refrigerant can cause you system to make sulfuric acid which will corrode and eat your system! For larger units over 5 tons, we suggest you use the Enviro-Safe Proseal XL4 Direct Inject. These are available in various of the larger sizes.