Newman's suggestion has a lot of merit.
It would not hurt to also verify the current consumption of the furnace while being bench tested, or as installed but powered from an external supply. It's theoretically possible that it could operate but still have a problem causing it to use too much current, such as a partly shorted solenoid or some motor trouble.
7.5A fusing provides rather little overhead for the furnace, which (at least according to some pictures of the model online) is rated to use 7A. Assuming the wire going to the furnace is reasonably sized, I might try a 10A fuse if everything otherwise checks out. Obviously, doing that is at your own risk...but it would have to be a very poorly done installation for it to be dangerous. The Suburban installation instructions recommend a 12 gauge wire for the furnace power feed.
