cruisair fan not switching on

[xluke]

Hello,
I have an older cruisair ac/heat pump with the rotary control panel and the fan has stopped switching on. The fan itself works because if I jump it she blows well. I suspect the problem is at the rotary control. Does anyone have suggestions as to how I might figure out if it's the rheostat or relay that's not working so I could replace that component, or other suggestions how I might fix this issue? A new rotary panel is nearly $500, which seems absurd.

Thanks!