Final answer:
To dehydrate the system after a major repair, evacuate the system to a minimum of 500 microns using a vacuum pump and closed service valves or process stubs.
Step-by-step explanation:
To dehydrate the system after a major repair, the recommended method is to evacuate the system to a minimum of 500 microns. This involves using a vacuum pump to remove any moisture or air from the system. Evacuation helps prevent issues like freezing, corrosion, and reduced system efficiency.
During evacuation, all service valves, access valves, or process stubs need to be closed to create an airtight seal. Once the vacuum pump is connected, it should be run until the pressure reading on the gauge reaches the desired level of 500 microns or below.