This is from "Carrier's" original handbook 1968.
To test small hermetic and semi-hermetic compressors used for medium and low temperature applications, the following method can be used to test for internal valve leakage.
1. Attach a low pressure gauge to the suction line service port.
2. Close the compressor off from the low side of the system by front seating the suction service valve.
3. Run the compressor for two minutes.
4. Turn off the compressor and observe the reading.
The compressor should have pulled down to at least 16 inches (410 mm) of Hg. If the vacuum reading starts weakening toward 10 inches (254 mm) of Hg vacuum, the discharge valves of the compressor may be leaking and will probably need to be replaced. If the compressor doesn't pull a vacuum below 16 inches Hg, the suction valves are weakening and may need to be replaced. If the compressor is welded or hermetically sealed and these conditions exist, a new compressor is the only possible remedy.