When dehydrating a system, it should be evacuated to a minimum level of;

The process of dehydrating a refrigeration or HVAC system requires that the system be evacuated to a level which ensures that all moisture is removed effectively. Achieving a vacuum of 500 microns is critical because moisture in a system can lead to several issues, including the formation of acids, ice, and other contaminants that can damage components and reduce efficiency.

The 500 micron threshold is generally accepted in the industry as a safe limit to minimize the presence of moisture. When the vacuum level reaches this point, it indicates that the system has been sufficiently degassed and has an extremely low amount of moisture, which is essential for maintaining system integrity and performance.

Higher levels, such as 30 inches of Mercury or 25,000 microns, do not effectively eliminate moisture, and a lack of regulatory backing from the EPA signals that at least some threshold must be adhered to for proper system operation. Therefore, targeting 500 microns is a well-established standard in practice.