Agreed pics will help with advice. BUT if you are not familiar with the operation of the furnace it would be good to have a repairman take a look at it. Most of these older units should be similar & someone with experience should have first hand knowledge even if you need to take it to them.
My 1982 MH (Newell not AS) has Suburban Furnaces. They sat for at least 7 years with no use and when I went to test them I simply pulled each one, mounted on a bench and plumbed them one by one. I found that Mud Daubers had built nests in two of the three & that hindered the fan operation. One of them needed a new Circuit Board so I went to Dinosaur Electronics for that;
http://www.dinosaurelectronics.com/
I would not replace simply to replace from non-use. There are professionals that can get these going if they are not in poor condition & would be able to advise.