I think its very important that the spal only controls one fans(variable) and the other fan with just an on/off switch. There should be a relay for the second fan. The Spal should only switches the second fan on when it reaches the high setting, thus full blast only for the second fan. If the previous owner connected both fans to the spal's variable output, the fans may be overloading the controller. From the spal specs, the controller is good for about 30amps, and it seems that the FAL duals draw more than that, which why they recommend a relay for the second one. follow the wiring of both fans to see where they lead. One of them should take you to an external relay. Let us know