norcold n611???

have a 14 year old norcold mod N611, it keeps giving me 5 green blinks on the panel which means that the cooling unit has stopped working. i reset the control board and turn back on and it works for a few hours and get cold and than goes into the 5 green blinks again shutting it down. have reset 3 times and still have the problem.
anyone have any ideas what else to do or look for?
thanks