When evacuating an A/C system, how long should the vacuum pump remain on after reaching a certain mercury level?

When evacuating an A/C system, it is essential to achieve a deep vacuum to remove moisture and non-condensables from the system. The correct answer indicates that after reaching a vacuum level of 26 to 29 inches of mercury, the vacuum pump should remain on. This level of vacuum is typically considered sufficient to ensure that any moisture or contaminants are adequately removed, which is critical for the system’s efficient operation and longevity.

The standard practice in the industry recommends holding the vacuum pump at this level for a period, usually around 30 minutes to an hour, to guarantee that the system is thoroughly evacuated. A vacuum reading between 26 to 29 inches of mercury demonstrates that the system has achieved a substantial reduction in pressure, which significantly decreases the boiling point of any remaining moisture and helps in its removal.

Achieving this level ensures that the A/C system can operate effectively without the issues related to water or air in the refrigerant lines, which could lead to ice formation inside the system or reduce the efficiency of the cooling process.