I am new and learning the system. When I ask this coworker whether he has time to talk about some questions I have, he always answers yes. Sometimes he clearly means it and we talk in-depth about my questions, almost always giving me the information I was looking for. But at other times he clearly doesn't actually have time. He says he's free to talk but then his answers are very short and very general, and he looks politely impatient to return to what he was doing.
The really hard part about this pattern is that when he doesn't really answer my questions because he's busy, it makes me feel like it would be awkward to approach him at a later time to ask pretty much exactly the same set of questions that weren't answered before. So now I've got unanswered questions that I feel I can't ask.
How can I ask "Do you have time to talk?" such that he feels like he can reply in the negative if he's busy? It seems he's not comfortable saying no, as if it's socially unacceptable. I don't feel that way and have no problem telling someone "I'm in the middle of something can you come back in ten minutes?" and I wish I could make him feel comfortable saying that too.