Conditioned Air Temperature Control System Component Location  5C8 
21-61-0  Figure 1 (Sheet 1)  Feb 20/88 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

5C8  Conditioned Air Temperature Control Systems Component Location 
Jun 20/85  Figure 1 (Sheet 2)  21-61-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

F.  Each temperature control system includes an air mix (temperature control) valve, a 190°F (88°C) duct overheat thermal switch, a 250°F (121°C) duct overheat thermal switch, a pack switch, and both manual and automatic temperature regulating circuits (Fig. 1).
G.  The manual temperature regulating components consist of two cam-operated switches, in the temperature selector assembly, which are electrically connected to the mix valve actuator. The automatic temperature regulating components include a third cam-operated switch in the temperature selector assembly, a regulator, cabin temperature sensor, anticipator sensor, and a duct temperature limiting sensor.
2.  Air Mix Valve
A.  The mix valve consists of two butterfly valves operated by the same actuator through a common shaft. The 115 volt ac actuator mounts on a flange of the hot valve to drive the common shaft. When the hot valve butterfly is full open the cold valve is full closed and vice versa. As the hot valve moves toward close the cold valve moves proportionally toward open. A position potentiometer is connected to the opposite end of the shaft from the actuator to permit monitoring the valve position from the control cabin. A visual indicator is also located at the actuator between the potentiometer and the cold valve body (Fig. 2).
B.  Limit switches in the actuator housing interrupt current to the actuator motor at either extremity of travel. The mix valve is located in the air conditioning equipment bay inboard of the heat exchangers.
3.  Thermal Sensing Units
A.  Thermal sensing units in the temperature control system consist of thermal switches, temperature bulbs, and temperature sensors. Thermal switches are used to protect against duct overheat, temperature bulbs are used in conjunction with indicators for monitoring passenger cabin temperature and passenger cabin supply duct temperature, and temperature sensors are used with the automatic temperature regulation systems to automatically position the mix valves in obtaining selected temperatures for the cabins.
B.  The thermal switches consist essentially of a bimetal element enclosed in a steel probe. The thermal switch contacts are normally open. At a predetermined temperature the contacts will close. A 190°F (88°C) passenger cabin duct overheat thermal switch and a 250°F (121°C) passenger cabin duct overheat thermal switch are used in each control system. The switches are mounted in the main distribution manifold (Fig. 1).
508 
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511  Air Mix Valve 
Aug 15/68  Figure 2 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-61-0 Page 5 

C.  Temperature bulbs consist of a temperature sensitive resistance element within a tube. As the temperature of the element changes, its resistance changes accordingly to cause movement of an indicator pointer.
(1)  
The passenger cabin temperature bulb is installed with the passenger cabin temperature sensor inside a sensor duct (box) located below the stowage compartment (Detail A, Fig. 1). A tube connects the box to the auxiliary power unit (APU) compartment on Passenger/Cargo Convertible Airplanes and to a small in-line fan on Standard Passenger Airplanes. The low pressure in the APU compartment and small in-line fan draws air from the cabin across the bulb and sensor.

(2)  
The passenger cabin supply duct temperature bulb is mounted in the main distribution manifold.

D.  The temperature sensors also utilize variable resistance type elements. As temperature increases, their resistance decreases and vice versa. The sensors form a part of the automatic regulation system network to maintain selected temperatures in the control and passenger cabin. A duct limit temperature sensor, anticipator sensor, and cabin temperature sensor are used with each regulation system. The duct limit sensors and anticipator sensors are mounted in the main cabin distribution manifold.
(1)  
The control cabin temperature sensor is located behind a screened opening in the ceiling, approximately 4 inches left of center, at station 259. A tube connects the sensor box to the equipment cooling duct (Fig. 1). The low pressure in the equipment cooling duct draws air from the control cabin across the sensor.
　
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