I thought you stated previously that you replaced the Upper board and tstat with a 5 button system? Is the complete unit going dead? Both the compressor AND Fan shut off? If so, I suspect your control board is not good or set up correctly. If they shut down(both) you are losing 120 power to the unit. If you still have the original 4 button system, then I will bet you either have a LOOSE 120 wiring where they connect with wire nuts at the upper board or the control board 120 connections are bad. Doug
icing up will not stop the fan from running. Also, your model has a Freeze sensor(I hope you installed that part when changing out the AC unit.