Rick-
Certainly one of the topics discussed in this thread could be related to your faulty fan, but our coach wasn't very old when I discovered one of ours inoperative. It was merely a poorly placed wire connector, and pinched wire, at the fan itself. So if it's a heat exchange unit that's reasonably accessible, I'd find checking it's fan's wire connectors a relatively easy first step.
After checking the integrity of the wires there, turn the heat on in that zone and probe the connectors with a voltmeter to verify its getting juice or not before searching for fuses and such upstream.
Joel