This is a problem which has been reported in various forms for multiple years of the MDX, and with various possible solutions (most of which don't work in general, but do work in specific instances). The A/C (mode, AC, and fan buttons) do not work when pressed, and the external temperature does not display. Looking at the Nav. diagnostic screen shows the AC (climate control computer) has failed. Sometimes re-loading the software from the disk fixes the problem. On my 2002 MDX, this didn't work. What does appear to have worked is pulling fuse # 3 from the drivers side fuse box and then putting it back in (the fuse is still good). This fuse controls the AC and fan relays. Why this worked I don't know. It's possible that it's coincidence. It may also have caused the climate control to reset itself. Does anyone have a good, authoritative, solution for this problem?