AP 320 A La Carte works on and off

[BriceB]

I have had this AP 320 frozen food machine for about 3 months and it always seems to end up at like -20F and going "out of service". The compressor would continue to run. The temp is set to +10F. I sent the refrigeration board in for repair because that's what vendors exchange recommended. When I reinstalled the board the machine worked well for a solid week, then it went down to -20F again. I reset the machine and it worked well for another week, and then it went out of service again and is staying right about +20F and won't get any colder. There is lots of ice in the back of the machine. It doesn't seem to defrost very well. I'm looking for any advice to get this machine working steadily.