Refrigeration & Air Conditioning Mechanic Red Seal · Question
A technician is evacuating a large commercial low-temperature system. After pulling a vacuum for several hours, the vacuum gauge settles at 500 microns. The next morning, the gauge reads 1500 microns. What is the most likely cause for this pressure rise?
A significant rise in vacuum pressure overnight after achieving a deep vacuum (500 microns to 1500 microns) typically indicates the presence of moisture. The mo
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Question: A technician is evacuating a large commercial low-temperature system. After pulling a vacuum for several hours, the vacuum gauge settles at 500 microns. The next morning, the gauge reads 1500 microns. What is the most likely cause for this pressure rise?
Answer options:
- The vacuum pump oil needs to be changed.
- There is a refrigerant leak in the system. ✅ Moisture is still present in the system, boiling off over time.
- The vacuum pump has reached its ultimate vacuum.
Correct answer: Moisture is still present in the system, boiling off over time.
Explanation: A significant rise in vacuum pressure overnight after achieving a deep vacuum (500 microns to 1500 microns) typically indicates the presence of moisture. The moisture, under vacuum, continues to boil and release vapour, increasing the system's absolute pressure over time.
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Question explanations
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