The vacuum test requires a reading at the end of five minutes during which no more than blank inches of vacuum should be lost.

• A. 5
• B. 10
• C. 15
• D. 20

Answer: (B)

In this test, you’re checking how well the system holds a vacuum over a five-minute period. A vacuum is applied and you watch the gauge to see how much the reading drops. The amount of loss reflects how much air is leaking into the system through hoses, seals, gaskets, or fittings. The standard tolerance is that the vacuum should not be lost by more than 10 inches of mercury in five minutes. If the reading falls more than that, it means there are leaks that need to be found and repaired before service.

So, a loss of up to 10 inches is acceptable, while greater losses indicate leaks. Values like 15 or 20 inches would show significant leakage, and a loss as small as 5 inches would be unusually tight for a typical setup.