A local pilot sold us his Aspen setup; we got a PFD 1000 Pro and an ACU and had it installed by a reputable local shop. I flew it for about 4 hours and then the ACU suddenly died. There's effectively no way to troubleshoot these units in the field, so we had the shop pull it and get a replacement from Aspen (which has the nice benefit of giving us a 1-year warranty on the new one). For those of you who have had ACU failures in your aircraft, did you ever find a root cause? I'm a little nervous that some hidden problem with the install is going to kill the new one, too.