I agree with rynoattack that it really depends on the specifics. If it's a high level juco, and a high level NCAA D1, then the chances of good that the coach will be on board. If it's a juco that prides themselves on moving guys to D1, and you leave after one year to go to a D3, they probably won't be particularly happy about it. They may want you to stick around for a better offer after another year. For juco coaches, it's a balancing act between winning and placing guys at the next level.