Hello reefermechanic

I'm an reefer electrician but new to this job. I have a problem on a carrier reefer, model 69nt40-541-015 wich has a ML3 controller. In proximately one month it fried 2 controllers. I had the container not working at all, replaced the controller, it worked fine, did the PTI, went on a trip and when it returned it was just like the removed controller. sometimes it works but giving alarms, other times the display and reefer are completely dead. It has 2 pins on connector KA (KA9 and KA10) that are the power supply to the controller, ( 33V betwen them) I think. Does the controller have any other power supply? and if not do you think that the transformer can have some sort of problem? by the way do you know the language of programming used in these controllers? is it ladder or FBD or is it something mor complex like C++?