What cause one running out of you home to be melt and the other conclusion freezing? I have a double widespread mobile home and the end where on...

I have a double widespread mobile home and the end where on earth the furnace is located is very hot and the thaw air blows through the vent good, but the other ending of the house is freezing, what could be the cause of this. I have a guy check the duct underneath and he said both were on but the upper air is barely coming through the vent on that one end of the house. That duct be put on back contained by 2003. Anyone have any thought what else it could be.
Dead animal between the walls?
Answers:    try and close some of your vents on the heat up side of your home to force more warm nouns to the cool side.
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bad insulation