Most pumps have a check valve built into them to prevent this from happening. If your pump does not have this feature, you can fabricate one yourself. You should be able to get parts at a supplier.
If you are diligent about changing your oil after each pump down, It would not be too much of a problem in older mineral oil systems. In new POE systems it could be.....
lets us see what other people have to say about this issue.
Yes it can and has happened. Always make sure you have a check valve. there was a tech who posted last year or so, asking how to get a couple of gallons of oil out of a absorber. His pump failed and the machine sucked all the oil in. This is usually the death for a absorbtion machine. At least for a Yazaki. Most of the chambers are stainless steal and dirty oil is not a good thing. In a split or package unit, you could flush, But would take allot of work to get it good and clean. Not to good for warrenty either. So why take the chance. Even if your pump oil is clean, as it should be, still not a good thing. I dont like to leave things unattended for to long. Big chillers that we have multiple pumps on and have to leave over night, we make sure that all pumps are in good condition and have working check valves.