Temperature control systems are used to modulate the temperature of the ventilating air entering an airplane cabin.
Valves and actuators are used to regulate temperature within an aircraft. Add-heat modulating valves are used in airplane air conditioning systems to control the pack discharge temperature, prevent icing within the system, and provide warming trim air for individual multi-zone systems. These functions are accomplished by mixing bleed air and refrigerated air in response to a sensed mixed air temperature. Butterfly valves are most used as add-heat valves; both electric-motor actuators and pneumatic actuators are commonly used to drive these valves