Fan controller took a ****, again!

Do you have the fans running right off the controller? I wonder if running the controller to a couple of relays would help. I know you said it was a high amp unit.... the instructions for the dual fan controller 16789 say 35 Amp continuous per fan. What model fan are you using?
Did the temp sender come with the controller?
From the instructions for the 16789
The green wire is designed to work in two different configurations. When used, this will allow Electric Fan #1 to be turned on
regardless of the temperature of the thermostat as it simply overrides all other functions

Hope Derale makes it right.