The science behind FCU systems utilizes fundamental principles of physics, especially thermodynamics laws, which govern processes related to heat transfer, like conduction and convection. Heat absorption occurs through its coil when refrigerant evaporates to cool down during cooling mode.
Concerning practical implications, the FCU system has air and refrigerant movement. In cooling mode, it takes up warmer air from this space and blows it over the coil. Therefore, the refrigerant removes heat from the air, thus cooling it off.
This cool air is then re-circulated into the room, cooling it effectively. However, in heating mode, the reverse process is adopted. Heat is removed from the refrigerant through the coil and transferred to the air, heating it before exhausting it back into the room.