Location is Northern SC. Utility providers: Duke Power & Piedmint Natural Gas.

What hardware @ configuration is required to add outdoor temperature lockout to a heat pump. Heat pump is Trane XR13. Supplemental heat is Trane ntural gas furnace. H-well Focus Pro thermostat. I believe system was installed and configured in a manner that, despite the outdoor temperature, when the system calls for heat the heat pump can run for around 30 minutes before switching to gas furnace supplemental heat (I'm using the terms supplemental heat & auxilliary heat interchangably here). Operation is OK until outdoor temp. drops to mid 20's. Then in the event the system runs (seems forever) and finally switches to supplemental and satisfies thermostat setpoint that just described must repeat cycle. In mid-20's outdoor temp. this obviously results in a lot of heat pump runtime.

Tiger & Ryan particularly, I'd appreciate your advice regarding possibility of adding outdoor thermocouple and control logic to lock out HP at specific temp. all advice welcome.