Dometic Thermal Fuse Thermocoupler

[3638FHBRDG]

Know this is a Dometic issue not Grand Design or Keystone:

Hope this helps someone else from this frustrating issue. Brand new 22 Cougar MLSWE with refer in slide. Purchased in late June 2021. We are now on our 4th Dometic Thermal Fuse Thermocoupler! Dealer would replace and run the refer on propane for days with no problem, yet if we picked it up and went for a trip, the Dometic Thermal Fuse Thermocoupler would blow. Finally had a 30 year RV tech finally be assigned our unit. He did some head scratching and discovered that either Keystone or Dometic changed the shape and molding profile of the black rectangular vents for the outside of the refrigerator back. He pulled an older model trailer unit so both were side by side so he could compare both for build and parts. He put both old and new black vents together and you can visually see how the moldings were done differently. His theory is with the new cover design and placement in the sidewall, when moving down the road a steam of air is directed right at the location of the flame at the bottom of the chimney of the gas unit creating sort of "blow torch" effect which created the burn mark on the chimney - hence, the excess of 305 degrees and the blown thermocoupler(s).
He created a metal shield or baffle that sits in front of the opening of the chimney where the gas line and other items go into the bottom of the chimney. It is short in height, and attaches to the bottom of the refer unit and the protective metal cover plate for the chimney. It runs perpendicular to the outside wall of the trailer blocking the stream of air while moving down the road.
Just tested with a freeway run of 60 miles plus. Kept my speed a little lower so the big simi's would blow past me at their speed and buffet the trailer with an air rush at the refer vent. Refer is on the driver’s side of the trailer. Refer is still working! That is the longest this refer has lasted without blowing the thermocouple since we bought it.
I know that it may be hard to visualize the part, the baffle is no bigger than 1/2 a playing card if that.. 2 images attached. The one w/o the baffle is showing an identical Keystone trailer (22MLS) that is new on the lot. The second photo shows the small installed baffle on our unit. Small and held in place w/2 sheet metal screws. Small enough so it does not restrict the needed air flow for the refer to work properly.
Hope this helps someone solve their issue.

[Wicked ace]

I just want to clear the air with some of the semantics used in this thread mostly because it bothers me.
First: There is no such thing as a "thermocoupler". That is a bastardization of the name given to a temperature measuring device called a THERMOCOUPLE. A Thermocouple is merely two pieces of dis-similar metal wires twisted together that will generate a voltage at defined temperatures and be read by a precise voltage meter.
Second: The item the OP and the previous poster point out as a problem device is a THERMAL FUSE designed to melt a current carrying element at a predetermined temperature range. It's a passive safety device, much like the draft element on the chimney that shuts down everything in case of high temperatures or more likely fire.

[MiniLiteMan]

Really good info that I found after the fact. I found the thermal fuse had opened after replacing both the Power Control Module and the Eyebrow boards. Good news is the repair was only $1.75 but I kept the Power Control Module I bought from Dinosaur Electronics in Oregon ($175) as part of my spares kit for the fridge. An expensive spare for sure but it is insurance from what a lot of people are saying eventually can and will fail.

[Mikec557]

Really good info that I found after the fact. I found the thermal fuse had opened after replacing both the Power Control Module and the Eyebrow boards. Good news is the repair was only $1.75 but I kept the Power Control Module I bought from Dinosaur Electronics in Oregon ($175) as part of my spares kit for the fridge. An expensive spare for sure but it is insurance from what a lot of people are saying eventually can and will fail.

Bummer you didn't find this thread in time. But your smart to keep the Dinosaur board. I think you will eventually need it. Except for Murphys law, now that you have one you'll never need it. LOL.

The OP