You're on the right track thinking the unit will not reverse to the A/C mode. However, it may not be the control board. There is a mechanical "switch" that does the reversing. It has been so long since I heard anyone complain about this I have forgotten the details. Before jumping into the control board, get a schematic and see if you can find the mechanical switch. I do not remember if the switch is replaceable or not. Sorry, I do not have the details, but this was a prevalent problem on units in your coaches age and older.
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