The cooling unit went out on my Norcold LMI 1200, went to a local dealer, they ordered and then installed the new cooling unit. I went away for a long weekend, the refer never got cool or cold. Cooling unit was running and getting hot but nothing was getting cold. Took it back, they tested and ordered another new cooling unit and installed. I didn't take the coach away this time, but the same thing happened again, cooling ran for awhile and then stopped, nothing got cool or cold. What could be the problem?