Thermo King KD 2 SR and MD 200 Electronic Help.

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.

start with the basics, check for a faulty fuel solenoid.
Remove the solenoid from the inj. pump (leave plug connected) and with a multimeter on the 8D wire at the plug monitor voltage.
start the engine, the plunger on the solenoid should pull in and 12volts present on 8D.
2 things could happen, (well actually 3, it could keep running :)
# voltage drops off then the plunger disengages. ( indicates power supply issue)
# plunger disengages, voltage still present. ( indicates faulty fuel solenoid)
Remember, you need to shut the eng. off manually when the fuel solenoid is removed, do this by pushing the tab in the back of the pump where the solenoid was.
Good luck!

u need to deal with the code 74, unit not configured correctly first.
you need the UPT green book to check the jumpers on the relay board and set up the unit correctly.
pm me

The hot relay issue will probably be the stop solenoid as tkman states, i'd be measuring amp draws personally.
Theres three wire coming out the solenoid, white=pull in, red=hold in and black=earth.

So it powers up the white wire first(to pull solenoid in to start), then starts and powers up red to hold the solenoid in and drops power to the white wire

You can connect the white wire to the starter motor, to the connector that the bigger wire from the starter solenoid connects to, like a carrier unit, this will bypass the draw on the relay board.

The solenoids can get full of oil making a high amp draw.

there is also a revised relay board and a thermo king bulletin on code 63's and these units

Thank you both for good info and advice. I will start on this later today if I can. I am very interested in the revised relay boards and bulletin on these units in regards to 63's. The solenoids seem dry but the large plugs do have a lot of grease and grass clippings in them. I will get some electric contact cleaner and clean them too.

I also have a different unit I think a TD 2 MAX with a issue where it runs good as long as the fuel pump is running. It intermittently dies or chugs and stumbles for a while then dies and when ever it does this the fuel pump is not running. Sometimes it does this right at start up and sometimes it does it after it runs for a while. My mechanic claims it needs a new fuel pump but I think the pump is fine its merely the the voltage supplied to it that is wacky. Possible the fuel pump solenoid. So I think I can use this info to diagnose that too maybe.