mabe im wrong but would think that if ya had ya temp set at say 77 its not gonna get colder than that so why a
If you have a chiller set to 77, it shouldn't get much warmer than 78, before it kicks on, it can easily get colder. The reason for a dual controller is to prevent the heater and chiller from running at the same time, thereby working against each other.
Aqualogic should make one. (858) 292-4773 is the number for aqua logic, call them and ask them what the model number is of the controller for you and where you might find one.