I have a 2 year old coleman evcon natural gas furnace (model number DGAA056BDTB) in my 12 x 60 mobile home. The indicator light is showing normal operation. Blower works fine and there is plenty of force in the air flow from the heat vents throughout home. The flame and ignition are also working fine. The problem is that once the furnace kicks on, the heat in the home does not heat above 60 degrees despite running for hours with flame in the chamber. The blower runs for hours. Temperature in home drops below 60 when outside temp drops below 40. Furnace repairman said gas pressure was fine. He called Coleman and was told I could do nothing to resolve the problem because the furnace was too big for my mobile home. Any ideas?