S: refm4023aa

This is not a chiller but it has the millieum controls, so i thought it was close enough. This unit everday or two shuts off, where the display screen goes blank. Voltage on the power board, 12dc on the control board. 12vdc on the display board but this unit is not doing nothing. I can hear an humming coming from the power board but nothing is hot or seems wrong. The large heat sink on the control board gets very hot, never noticed this before. I replaced the control board already, and a relay board. So the customer is pissed cause its still not working. It seems if i power down for 10 mintues it comes back on and says daily schedule shut, then comes back on. Any help thank you.