I read that it is important to “break the vacuum” on a vacuum pump immediately after evacuating an automotive a/c system and prior to charging to avoid damaging the pump. What exactly does that mean? I’m guessing that the vacuum is “broken” when the pump switched off and the utility hose is disconnected from the manifold set. Thank you. -Gary

The longer you leave an evacuated system sitting in a vacuum, the more risk you have of air and moisture getting pulled back into the system. You want to get the system positively pressurized as soon as possible. That is what is meant by breaking the vacuum. This is usually done by letting some of the refrigerant charge into the system – just enough to positively pressurize it. Before adding the rest of the charge, disconnect or isolate your vacuum pump and micron gauge to avoid damaging them with the full refrigerant pressure. Another reason to get your vacuum pump disconnected from an evacuated system quickly is that the vacuum in the system can siphon the oil out of a vacuum pump that has been switched off.