I'm not sure...I have always let my pump run for 20 to 30 minutes and then charge the system. Never had a problem with this method and I always replace the drier/receiver when I open the system.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

What is it going to hurt? The vacuum will help pull all that moister ladened air from the lines and the dryer and the evaporator,my uncle was a votec teacher for a/c and he was always telling me to let it pump,the longer the better! most customers cant wait around but if you can let it rip.JNT