Nu-Calgon - A/C EasyDry contains a dehydrating agent that converts system moisture into a natural organic material that is compatible with and mixes with the lubricant. We recommend the use of A/C EasyDry whenever there is a concern that a system has moisture. It can also be used prior to A/C EasySeal to ensure all moisture has been removed from the air conditioning system. The 3 oz. aerosol can is sufficient to treat systems up to 5 tons. In most cases, if a system has not leaked all the way to zero, there is typically no air or moisture in the system. When charged, the system has greater pressure than the outside atmospheric pressure and moisture and air will typically not enter the system. But in situations where the system is known to have moisture in it, use A/C EasyDry.