Hi I am a small Dairy Distributor that has about 15 refrigerated Bobtail Trucks. We have a mechanic that services our reefers and is great with the mechanic side to servicing them but is not very smart with the electrical side. I am really good with working on classic muscle cars and motors but admit don't know all that much on the units other then what I have had to replace in order to keep my trucks running and cold. My questions are for the units that keep shutting off continuously due to something that on each unit seems to be different but flashes a 63 code. My MD 200 will fire up and run fine for 15 minutes to an hour or sometimes more on cooler days then shut off and flash a 63. When you clear it out it fires right back up, runs on high speed then kind of pulls down a few rpms sometimes then shuts right back off and flashes 63. It will do this for another 20 to 30 times for it might run for another 15 mins to an hour. Sometimes it shuts off even quicker and flashes a 20 code but its more rare. My mechanic cant seem to figure it out and wants me to replace the unit with another one. The thing is its much newer then most of my other units and has very low hours. I have done some research and have watched it do its thing and think i know why its shutting off. It has a 41-4458 relay board in it and from what I can tell the very bottom relay gets really hot and trips. Once this relay is hot it trips more often. My question is it the relay board that may need to be replaced or rebuilt? Or can it be something really simple but very annoying like on our other units we have found loose grounds to throw all sorts of codes and cause it to shut off. What would I check for wiring issues to cause this relay to get much hotter then the other ones. It is the K7 On/Run relay. But it also has a 74 code that never clears out so that is why I think it might be the relay board. Any advice?

And I must say I would love to learn more about diagnosing problems with these units. Is there a way to hook up a laptop up to these units with proper software and cables that would make it easier to at least where to look for problems?

Some of the people on here seem to really know what they are talking about.