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At what pressure range does the technician valve off the vacuum pump when evacuating to a deep vacuum?

  1. 250-150 microns

  2. 500-300 microns

  3. 700-400 microns

  4. 900-600 microns

The correct answer is: 500-300 microns

When evacuating an HVAC system to achieve a deep vacuum, it is important to valve off the vacuum pump within a specific pressure range to ensure proper evacuation. The correct pressure range to valve off the vacuum pump is typically between 500-300 microns. This range ensures that the system is properly evacuated of moisture and non-condensables, helping to prevent system issues and ensuring optimal performance. The other pressure ranges mentioned in the different choices are outside the optimal range for valving off the vacuum pump during evacuation. Option A (250-150 microns), Option C (700-400 microns), and Option D (900-600 microns) fall outside the recommended pressure range for proper evacuation. Therefore, they are not the correct pressure ranges for valving off the vacuum pump during the evacuation process.