1. Contact with the electric department for stable working condition operation and record the  relative value.
2. Close the evacuate valve of the condenser .
3. Record the vacuum readings once per minute, lasting for 5 minutes, the standard rate of descent is 2mmHg / min (3kpa), and is not higher than 5mmHg / min (7kpa) at maximum.
4. After the test is qualified, the evacuate valve is opened.
5. During test, if the rate of descent of vacuum is very quick, it is required to stop the test to find the reason.