Hi @andya28832
Found this [https://www.searspartsdirect.com/model/4uz08e06x6-001428/frigidaire-fad704dwd5-dehumidifier-parts|wiring diagram] for a FAD704DWD5 model - (click on wiring diagram) that may help.
Perhaps changing the fan capacitor may solve the problem. Look on the fan capacitor to find its value and rating information and use that information to search online for replacements.
Usually with most fans that have capacitors attached, they are there to increase/decrease the amount of current to the fan motor thereby altering its speed.
Since the fan power supply comes from the CN4 connector on the mainboard it may be that by switching speeds it alters the amount of voltage/current to the fan but if the capacitor is faulty this may be enough to make it fail entirely.
Either that or there's a problem on the board. Check the board for any obvious component damage e.g. burnt out or heat stressed components.
BTW it seems that there's not too many parts available for the dehumidifier, only 3 and none electrical. Even when looking at the [https://www.searspartsdirect.com/search?q=fad704dwd|exact model] you posted it states ''no parts.'' Also all the -dwd models listed i.e. dwd1→ dwd11 have the same wiring diagram.