aintnothin wrote:
Sam Spade, it gets its oil from the engine.
So maybe you shouldn't have confused the question by talking only about the compressor and instead asked the real question: What kind of oil does the engine use?
A lot of recent engines have that clearly marked on the cap that you remove to add oil. The maker of the ENGINE could also supply that information; so could the maker of the motorhome.
And I think your assumption about Cummins does them a dis-service.
In my few dealings with them they have always been friendly and helpful.
I suggest that you should try to get an owners manual for your unit. That should save you a LOT of time in the future.