This is not a Freightliner issue - the chassis systems have nothing to do with the furnaces or coach climate control. What brand of coach is it? I'll move the question to the appropriate brand forum and perhaps another owner of your brand of coach will have some experience with this sort of problem.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC