Type II — High-PressureQuestion 129 of 240
A technician performs triple evacuation on a Type II system. What gas is used to break the vacuum between evacuations?
a.Oxygen
b.Dry nitrogen
c.Compressed shop air
d.Carbon dioxide from a fire extinguisher
Explanation
Dry nitrogen is used to break the vacuum between evacuations because it is inert, moisture-free, and helps sweep out remaining moisture. Oxygen is dangerous because it can react explosively with refrigeration oil, and shop air adds moisture. Triple evacuation with nitrogen dilutes and removes noncondensables and water vapor more effectively than a single pull-down.
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