I sympathise with both parties. The new recruit obviously agreed to join you with very little understanding of what was involved - surely those who appointed him should have done a better job on this? - and probably isn't very happy. But you too have a just cause for complaint in that no governing body these days can manage if all members don't play a full part. Ideally, you should have some kind of introductory package or briefing session which would make clear your expectations of each other. We have a right to expect the best and have high standards - not making excuses on the ground that we are volunteers. We can leave at any time, so if we accepted an important job we must either do it or make way for someone who can live up to the high status of volunteering. Individually, we may be volunteers, but the governing body is no more a voluntary body than a magistrates' court.
Having missed the first opportunity to make your expectations clear, you have to find some other way, and I hope that you have an obvious colleague to do this. Ideally, it should be another foundation governor or perhaps your chair. Just say pleasantly to your new member that, now he has settled in, you hope he will accept his share of the tasks - including becoming familiar with the school at work, being on a minimum number of committees and doing his share of appointments and other recurring chores. Perhaps he would like to sit in on a few non-confidential committees to find out what interests him? Do start treating the first meeting in the autumn - when you will in any case be reviewing committee membership and other duties - as one in which you remind yourselves of certain basic expectations of work-sharing, important working-together and behaviour principles, school visits, discretion about things you may hear about people's private affairs from your contact with the school, and so on. We all need it, and it is a time when you can put things right without involving individuals if you make it a routine.
And would someone - your chair or an experienced foundation governor - remind those who make appointments that the work-load is heavy and must be shared, and that you hope possible recruits will not be under any misapprehensions.