How can I add oil to a compressor?

[kengineering]

I was working on a refrigerated display case made by AKE of Europe. The system had a restriction in the liquid line just after the filter drier. In the process of troubleshooting and repair I was putting dry nitrogen through the lines to insure the restriction was clear when a slug of oil shot out and made quite a mess. Oil poured out of the tubing and it was not possible to measure the amount however I would venture to guess it was maybe 1 to 3 ounces. The Danfoss specs state it requires 18.5 ounces of POE. There are no service valves, only a schrader on the process tube.
Questions; 1) How much oil loss would cause a critical effect? 2) If I knew how much oil was lost and wanted to top it off how would I go about it with only a schrader on the process tube?
Thanks Ken..

[Brian_UK]

Use an oil pump to inject oil into the system.

Or

As the system is 'empty' now why not fit an additional access port so that you can place the system under a vacuum and use the vacuum to suck oil into the process tube.

[kengineering]

Thanks The vacuum worked just fine. Ken