With the advances in technology the volume of electronic components within an aircraft has risen exponentially. Since these components are powered continuously while the aircraft is operational, they continuously dissipate heat and are these equipment's should not exceed certain temperatures just like the cockpit they need to be cooled.
The avionic system thermal control system is required to deliver to the individual equipment the temperature and coolant flow rate required to maintain equipment semiconductor junction temperatures at the levels required to meet reliability and performance requirements
These systems differ by their coolants as Air Cooled Avionic Systems and Liquid Cooled Avionic Systems.