Why must an A/C system be evacuated before brazing?

An A/C system must be evacuated before brazing primarily to remove moisture from the system. This is critical because moisture can lead to the formation of acids and ice within the system, which can cause significant damage to the A/C components and hinder the system's overall performance.

When the system is evacuated, it creates a vacuum that draws out any residual moisture and air. This process ensures that when the system is charged with refrigerant later, it will remain free from contaminants that could negatively affect the refrigerant's operation.

Brazing without proper evacuation could lead to issues like corrosion or freezing within the expansion device, ultimately compromising the cooling efficiency of the system. Thus, correctly evacuating the A/C system prior to brazing is a crucial step in maintaining the integrity and longevity of the equipment.