I've seen linesets thru duct numerous times.
Since the lineset was run through a hole in the furnace unit, and the front of unit is flush to the wall, that's the only place they could run the lines. no where outside the unit to run them sometimes.
designer of the trailer persons running the duct at factory screwed up and ran the duct under the front of furnace.
trailer duct is crummy anyway, look like hacked w/ scissors and tap ins beat into top of ducts, but at least they could seal the hole.
I too have seen lines running through the duct in mobile homes. Refrigerant lines, water lines, electrical lines, etc
through the duct line set
Hate to tell you but the orginal poster is 100% correct i have built serviced and worked on all types of mobile homes aka Manufactured homes the correct term since 1995 when homes have to be built to code.
my own furance in fact has the oil line comeing in through the out side air duct the burner pulls its air from but i have sinced changed this to the proper opening the maker provided for it.
you would be shocked at what i have seen over the years in thise old homes.
20 amp brakers on 14/2 wire
2 bathroom outlets tied in via the out side service outet.
you name it the list goes on and on
Originally Posted by PalmettoMaintPro